pcvx-20251231

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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

______________________________________________________________

FORM 10-K

______________________________________________________________

(Mark One)

For the fiscal year ended December 31, 2025

For the transition period from _________ to ___________

Commission File Number 001-39323

______________________________________________________________

VAXCYTE, INC.

(Exact name of Registrant as specified in its Charter)

______________________________________________________________

825 Industrial Road, Suite 300San Carlos, California 94070

(Address of principal executive offices) (Zip Code)

Registrant’s telephone number, including area code: (650) 837-0111

______________________________________________________________

Securities registered pursuant to Section 12(b) of the Act:

Title of each class TradingSymbol(s) Name of each exchange on which registered

Common Stock, $0.001 par value per share PCVX The Nasdaq Stock Market

Securities registered pursuant to Section 12(g) of the Act: None

Indicate by check mark if the Registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act. Yesx No o

Indicate by check mark if the Registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act. Yes oNox

Indicate by check mark whether the Registrant: (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the Registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yesx No o

Indicate by check mark whether the Registrant has submitted electronically every Interactive Data File required to be submitted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the Registrant was required to submit such files). Yesx No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer x Accelerated filer o

Non-accelerated filer o Smaller reporting company o

Emerging growth company o

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. o

Indicate by check mark whether the registrant has filed a report on and attestation to its management’s assessment of the effectiveness of its internal control over financial reporting under Section 404(b) of the Sarbanes-Oxley Act (15 U.S.C. 7262(b)) by the registered public accounting firm that prepared or issued its audit report. x

If securities are registered pursuant to Section 12(b) of the Act, indicate by check mark whether the financial statements of the registrant included in the filing reflect the correction of an error to previously issued financial statements. o

Indicate by check mark whether any of those error corrections are restatements that required a recovery analysis of incentive-based compensation received by any of the registrant’s executive officers during the relevant recovery period pursuant to §240.10D-1(b). o

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Act). YES ☐ NO x

The aggregate market value of the voting and non-voting common equity held by non-affiliates of the Registrant, based on the closing price of its Common Stock on the Nasdaq Global Select Market on June 30, 2025, the last business day of the Registrant’s most recently completed second fiscal quarter, was approximately $3.7 billion. Shares of the Registrant’s common stock held by each executive officer, director and holder of 10% or more of the outstanding common stock have been excluded in that such persons may be deemed to be affiliates. This calculation does not reflect a determination that certain persons are affiliates of the Registrant for any other purpose.

The number of shares of Registrant’s Common Stock outstanding as of February 20, 2026 was 143,920,361.

DOCUMENTS INCORPORATED BY REFERENCE

Part III of this Annual Report on Form 10-K incorporates information by reference from the registrant’s definitive proxy statement to be filed with the U.S. Securities and Exchange Commission pursuant to Regulation 14A, not later than 120 days after the end of the fiscal year covered by this Annual Report on Form 10-K, in connection with the registrant’s 2025 annual meeting of stockholders.

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Page

PART I

Item 1. Business 1

Item 1A. Risk Factors 52

Item 1B. Unresolved Staff Comments 95

Item 1C. Cybersecurity 95

Item 2. Properties 96

Item 3. Legal Proceedings 110

Item 4. Mine Safety Disclosures 97

PART II

Item 6. [Reserved] 99

Item 7A. Quantitative and Qualitative Disclosures About Market Risk 120

Item 8. Consolidated Financial Statements and Supplementary Data 123

Item 9A. Controls and Procedures 154

Item 9B. Other Information 156

Item 9C. Disclosure Regarding Foreign Jurisdictions that Prevent Inspections 157

PART III

Item 10. Directors, Executive Officers and Corporate Governance 158

Item 11. Executive Compensation 158

Item 14. Principal Accountant Fees and Services 158

PART IV

Item 15. Exhibits, Financial Statement Schedules 159

All references in this Annual Report on Form 10-K to “we,” “us,” “our,” “the Company” and “Vaxcyte” refer to Vaxcyte, Inc. and our wholly-owned consolidated subsidiary, or, as the context may require, Vaxcyte, Inc. only.

“Vaxcyte,” “eCRM,” and other trademarks of ours appearing in this Annual Report on Form 10-K are our property. This Annual Report on Form 10-K contains additional trade names and trademarks of other companies. We do not intend our use or display of other companies’ trade names or trademarks to imply an endorsement or sponsorship of us by such companies, or any relationship with any of these companies.

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Special Note Regarding Forward-Looking Statements

This Annual Report on Form 10-K contains forward-looking statements about us and our industry that involve substantial risks and uncertainties. All statements other than statements of historical facts contained in this Annual Report on Form 10-K, including statements regarding our future results of operations or financial condition, business strategy and plans and objectives of management for future operations, are forward-looking statements. In some cases, you can identify forward-looking statements because they contain words such as “anticipate,” “believe,” “contemplate,” “continue,” “could,” “estimate,” “expect,” “intend,” “may,” “plan,” “potential,” “predict,” “project,” “seek,” “should,” “target,” “will,” or “would,” or the negative of these words or other similar terms or expressions. Forward-looking statements contained in this Annual Report on Form 10-K include, but are not limited to, statements about:

•our expectations regarding the potential benefits, spectrum of coverage and immunogenicity of our vaccine candidates;

•our expectations regarding our preclinical study results and prior clinical study results potentially being predictive of future clinical study results;

•the timing of the initiation, progress and potential results of our preclinical studies, clinical trials and our research and development programs;

•our ability to advance vaccine candidates into, and successfully complete, preclinical studies and clinical trials;

•the commercialization of our vaccine candidates, if approved;

•estimates of our future expenses, capital requirements and our needs for additional financing;

•our ability to compete effectively with existing competitors and new market entrants;

•our ability to establish and maintain intellectual property protection for our products or avoid claims of infringement;

•our and our third-party manufacturers’ manufacturing capabilities and the scalable nature of our manufacturing process;

•potential effects of extensive or changes in government regulation;

•the pricing, coverage and reimbursement of our vaccine candidates, if approved;

•our ability and the ability of our third-party contract manufacturers to operate and continue operations;

•our ability to hire and retain key personnel;

•our ability to obtain additional financing; and

•the volatility of the trading price of our common stock.

Actual events or results may differ from those expressed in forward-looking statements. You should not rely on forward-looking statements as predictions of future events. We have based the forward-looking statements contained in this Annual Report on Form 10-K primarily on our current expectations and projections about future events and trends that we believe may affect our business, financial condition and operating results. The outcome of the events described in these forward-looking statements is subject to risks, uncertainties and other factors described in the section titled “Risk Factors” and elsewhere in this Annual Report on Form 10-K. Moreover, we operate in a very competitive and rapidly changing environment. New risks and uncertainties emerge from time to time, and it is not possible for us to predict all risks and uncertainties that could have an impact on the forward-looking statements contained in this Annual Report on Form 10-K. The results, events and circumstances reflected in the forward-looking statements may not be achieved or occur, and actual results, events or circumstances could differ materially from those described in the forward-looking statements.

In addition, statements that “we believe” and similar statements reflect our beliefs and opinions on the relevant subject. These statements are based on information available to us as of the date of this Annual Report on Form 10-K. While we believe that information provides a reasonable basis for these statements, that information may be limited or incomplete. Our statements should not be read to indicate that we have conducted an exhaustive inquiry into, or review of, all relevant information. These statements are inherently uncertain, and investors are cautioned not to unduly rely on these statements.

The forward-looking statements made in this Annual Report on Form 10-K relate only to events as of the date on which the statements are made. We undertake no obligation to update any forward-looking statements made in this Annual Report on Form 10-K to reflect events or circumstances after the date of this Annual Report on Form 10-K or to reflect new

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information or the occurrence of unanticipated events, except as required by law. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments.

Summary of Risks Affecting Our Business

Our business is subject to numerous risks and uncertainties, including those discussed more fully in the section titled “Risk Factors” in this Annual Report on Form 10-K. These risks include, but are not limited to, the following:

•We are in the clinical or preclinical stages of vaccine development and have a limited operating history and no products approved for commercial sale, which may make it difficult for you to evaluate the success of our business to date and to assess our future viability.

•We have incurred significant net losses since inception and anticipate that we will continue to incur substantial net losses for the foreseeable future. We currently have no source of product revenue and may never achieve profitability. Our stock is a highly speculative investment.

•We will require substantial additional funding to finance our operations, which may not be available to us on acceptable terms, or at all. If we are unable to raise additional capital when needed, we could be forced to delay, reduce or terminate certain of our development programs or other operations.

•Our approach to the discovery and development of our vaccine candidates is based on novel technologies that are unproven, which may expose us to unforeseen risks, require us to modify processes, and make it difficult to predict the time and cost of vaccine candidate development and the timing to apply for and obtain regulatory approvals.

•Our vaccine candidates are in clinical or preclinical stages of development and may fail in development or suffer delays that materially and adversely affect their commercial viability. If we are unable to complete development of or commercialize our vaccine candidates or experience significant delays in doing so, our business would be materially harmed.

•The U.S. Food and Drug Administration ("FDA") may disagree with our regulatory plan, and we may fail to obtain regulatory approval of our vaccine candidates.

•Our business is highly dependent on the success of our pneumococcal conjugate vaccine ("PCV") candidates. If we are unable to successfully develop, obtain approval for and effectively commercialize our PCV candidates, our business would be significantly harmed.

•Our primary competitors have significantly greater resources and experience than we do, which may make it difficult for us to successfully develop and commercialize our vaccine candidates, or may result in others discovering, developing or commercializing products before or more successfully than us.

•We may not be successful in our efforts to use our cell-free protein synthesis platform to expand our pipeline of vaccine candidates and develop marketable products.

•We currently rely on third-party manufacturing and supply partners to supply raw materials and components for, and the manufacture of, our preclinical and clinical supplies as well as our vaccine candidates. Our inability to procure necessary raw materials or to have sufficient quantities of preclinical and clinical supplies or the inability to have our vaccine candidates manufactured, including delays or interruptions at our third-party manufacturers, or our failure to comply with applicable regulatory requirements or to supply sufficient quantities at acceptable quality levels or prices, or at all, would materially and adversely affect our business.

•The FDA regulatory approval process is lengthy and time-consuming, and we may experience significant delays in the clinical development and regulatory approval of our vaccine candidates.

•The development, review and approval of our product candidates are subject to the operational capacity, processes and resource levels of regulatory authorities, which may fluctuate over time and could delay or adversely affect our business.

•If we are unable to obtain and maintain patent protection for our technology and products, or if the scope of the patent protection obtained is not sufficiently broad, we may not be able to compete effectively in our markets.

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PART I

Item 1. Business.

Overview

We are a clinical-stage vaccine innovation company engineering high-fidelity vaccines to protect humankind from the consequences of bacterial diseases. We are re-engineering the way highly complex vaccines are made through the XpressCFTM cell-free protein synthesis platform. Unlike conventional cell-based approaches, our system for producing difficult-to-make proteins and antigens is intended to develop and deliver high-fidelity vaccines with enhanced immunological benefits that are beyond the capabilities of conventional approaches.

Vaccines are one of the most successful and cost-effective global health interventions and prevent millions of deaths worldwide each year. Routine pediatric vaccinations in the United States are estimated to prevent approximately 17 million cases of disease over the lifetimes of each annual birth cohort, and it is estimated that every $1 spent on childhood vaccination results in savings of approximately $11. Adult vaccination has increased with the introduction of new vaccines along with expanded age recommendations and growing international adoption, which is contributing to the growth of the overall vaccine market. Given the critical role vaccines play in preventing disease from childhood through adulthood, the global vaccine market is large, durable and growing. There are areas of significant unmet medical need, including vaccines that can provide broader protection, against both currently circulating and historically prevalent strains, than currently marketed vaccines and novel vaccines that target pathogens for which there are no currently approved vaccines. We are driven to eradicate or treat invasive bacterial infections, which have serious and costly health consequences when left unchecked.

We carefully select our target disease areas and vaccine candidates based on the following criteria: areas of significant unmet medical need, clear commercial opportunity and efficient market adoption, acceptable biological risk and established or acceptable clinical pathways. We are leveraging our scalable cell-free protein synthesis platform to develop potentially superior and novel conjugate and protein vaccine candidates for adult and pediatric indications using these criteria.

Our pipeline includes:

•PCV candidates that we believe are among the broadest-spectrum PCV candidates currently in development, targeting the approximately $8 billion global pneumococcal vaccine market. Pneumococcal disease ("PD") is an infection caused by Streptococcus pneumoniae bacteria. It can result in invasive pneumococcal disease (“IPD”), including meningitis and bacteremia, and non-invasive PD, including pneumonia, otitis media and sinusitis. Our broad-spectrum, carrier-sparing PCV candidates, VAX-31, VAX-24 and VAX-XL, are designed to improve upon standard-of-care PCVs for both adults and children by covering the serotypes that are responsible for increasing portions of IPD in circulation and are associated with high case-fatality rates, antibiotic resistance and meningitis, while maintaining coverage of previously circulating strains that are currently contained through continued vaccination.

◦PCV Franchise Adult Indication:

▪VAX-31 is a 31-valent, broad-spectrum, carrier-sparing investigational PCV being developed for the prevention of IPD and pneumonia. VAX-31 is the broadest-spectrum PCV in the clinic, and has the potential to provide protection against both currently circulating and historically prevalent serotypes. VAX-31 was designed to increase coverage, in a single vaccine, to approximately 95% of IPD and approximately 88% of pneumococcal pneumonia circulating in adults in the United States aged 50 and older, with the potential to provide an incremental 14-34% of coverage for IPD and an incremental 19-31% of coverage for pneumococcal pneumonia over current standard-of-care adult PCVs.

•In September 2024, we announced positive topline results from a Phase 1/2 study of VAX-31 in adults. The VAX-31 Phase 1/2 clinical study was a randomized, observer-blind, active-controlled, dose-finding clinical study designed to evaluate the safety, tolerability and immunogenicity of a single injection of VAX-31 at three dose levels (Low, Middle and High) and compared to Prevnar 20® ("PCV20") in 1,015 healthy adults aged 50 and older. In the Low, Middle and High Doses, all serotypes were dosed at 1.1mcg, 2.2mcg and 3.3mcg, respectively, except serotypes 1, 5 and 22F, which were dosed at 1.65mcg, 3.3mcg, and 4.4mcg, respectively. The Phase 1 portion of the study included 64 healthy adults 50 to 64 years of age and the Phase 2 portion included

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951 healthy adults 50 years of age and older. The immunogenicity objectives of the study included an assessment of the induction of antibody responses at Month 1, based on opsonophagocytic activity (“OPA”) and immunoglobulin G ("IgG"), at each of the three VAX-31 doses and compared to PCV20 for the 20 serotypes in common, as well as for the additional 11 serotypes contained in VAX-31, but not in PCV20.

In the Phase 1/2 study, VAX-31 was observed to be well tolerated and demonstrated a safety profile at all doses studied through the full six-month evaluation period similar to PCV20. VAX-31 showed robust OPA immune responses for all 31 serotypes at all doses studied. At the Middle and High Doses, VAX-31 met or exceeded the regulatory immunogenicity criteria for all 31 serotypes and, at the Low Dose, for 29 of 31 serotypes. At the VAX-31 High Dose, average OPA immune responses were greater for 18 of 20 serotypes compared to PCV20 (geometric mean ratio (“GMR”) greater than 1.0), with seven of these serotypes achieving statistically higher immune responses compared to PCV20. At the Middle Dose, 13 of 20 serotypes had a GMR greater than 1.0 and five serotypes achieved statistically higher immune responses compared to PCV20. At the Low Dose, 18 of 20 serotypes met the OPA response non-inferiority criteria, 8 of 20 serotypes had a GMR greater than 1.0 and three serotypes achieved statistically higher immune responses. For all 11 incremental serotypes unique to VAX-31, and not in PCV20, all three doses met the superiority criteria.

Based on these positive results, we selected the High Dose of VAX-31 to advance to an adult Phase 3 program.

•In November 2024, we announced that the FDA granted breakthrough therapy designation ("BTD") for VAX-31 for the prevention of IPD in adults and, in August 2025, we announced that the FDA expanded the BTD for VAX-31 to include the prevention of pneumonia caused by Streptococcus pneumoniae.

•In December 2025, following an FDA End-of-Phase 2 meeting, we announced that the first participants were dosed in a Phase 3 pivotal, non-inferiority trial evaluating VAX-31 for the prevention of IPD and pneumonia in adults compared to standard-of-care PCVs ("OPUS-1"). We expect to announce topline safety, tolerability and immunogenicity data from this study in the fourth quarter of 2026.

•In January 2026, we announced the initiation of an additional Phase 3 trial evaluating VAX-31 when administered concomitantly with a licensed, high-dose seasonal influenza vaccine in pneumococcal-naïve adults aged 50 years and older (“OPUS-2”). In February 2026, we announced the initiation of a separate Phase 3 study evaluating VAX-31 in adults previously vaccinated with a lower-valency pneumococcal vaccine (“OPUS-3”). We expect to report safety, tolerability and immunogenicity data from the OPUS-2 and OPUS-3 studies in the first half of 2027. We are also planning for a manufacturing consistency study (e.g., a lot-to-lot study).

◦PCV Franchise Pediatric Indication:

▪VAX-31 is a 31-valent, broad-spectrum, carrier-sparing investigational PCV also being developed for the prevention of IPD in children. VAX-31 is the broadest-spectrum PCV in the clinic designed to cover approximately 92% of IPD in U.S. children under five years of age and approximately 96% of otitis media due to Streptococcus pneumoniae in U.S. children five years of age or under.

▪In December 2024, we announced that the first participants were dosed in the first stage of a Phase 2, randomized, dose-finding study of VAX-31 in infants. Stage 1 of the study evaluated the safety and tolerability of VAX-31 at three dose levels (Low, Middle and High) and compared to PCV20 in 48 infants in a dose-escalation approach. In the Low, Middle and High Doses, all serotypes were dosed at 1.1mcg, 2.2mcg and 3.3mcg, respectively, except serotypes 1, 5 and 22F, which were dosed at 1.65mcg,

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3.3mcg, and 4.4mcg, respectively. Participants who received VAX-31 in Stage 1 continued the standard dosing regimen as part of Stage 2.

▪In February 2025, we announced that the Phase 2, randomized, dose-finding study of VAX-31 in healthy infants had advanced to the second stage of the study. Stage 2 of the study is evaluating the safety, tolerability and immunogenicity of VAX-31 at the same three dose levels evaluated in Stage 1 and compared to PCV20. In line with recommendations from the ACIP, the study design includes a primary immunization series consisting of three doses given at two months, four months and six months of age, followed by a subsequent booster dose at 12-15 months of age.

▪In September 2025, we announced advancement of the VAX-31 infant Phase 2 randomized, dose-finding study to the third and final stage following modifications to the protocol to add a new dose arm to evaluate a VAX-31 Optimized Dose (majority of serotypes dosed at 4.4mcg and the balance dosed at 3.3mcg) and discontinue enrollment in the Low Dose arm. The Middle and High Dose arms continued as planned.

▪The modified study is evaluating the safety, tolerability and immunogenicity of VAX-31 and compared to PCV20 in 900 participants, including the 100 participants previously enrolled in the Low Dose arm.

▪In January 2026, we announced that we completed enrollment of this study. We expect to announce topline safety, tolerability and immunogenicity data from the primary three-dose immunization series and booster dose either sequentially or together by the end of the first half of 2027.

▪Pending the VAX-31 Phase 2 infant study readout, we plan to initiate a Phase 3 program in infants with an Optimized Dose formulation of VAX-24 or VAX-31.

▪VAX-24 is a 24-valent, broad-spectrum, carrier-sparing investigational PCV being developed for the prevention of IPD in infants, and it covers more serotypes than any pneumococcal infant vaccine on the market today.

•In March 2025, we announced positive topline, interim data from the VAX-24 infant Phase 2 study, a randomized, observer-blind, dose-finding two-stage clinical study evaluating the safety, tolerability and immunogenicity of VAX-24 in healthy infants that enrolled 803 participants.

•In November 2025, we announced final safety, tolerability, and immunogenicity results from the VAX-24 infant Phase 2 study that were consistent with the positive interim data reported in March 2025 and showed that VAX-24 elicited robust, dose-dependent immune responses, with little to no evidence of carrier suppression observed. The final data analysis included full 6-month safety results and complete post-dose 3 (primary immunization series) and post-dose 4 (booster dose) IgG and OPA results. The key immunogenicity endpoints included an assessment of immune responses for each of the VAX-24 dose levels (Low, Mid, Mixed) in comparison with PCV20 for the 20 common and 4 unique serotypes in VAX-24. At 1-month post-dose 3 and post-dose 4, immune responses were assessed based on serotype-specific IgG seroconversion rates (IgG threshold value of ≥0.35mcg/mL). IgG GMRs were also assessed at 1-month post-dose 3 and post-dose 4, along with other key immunogenicity endpoints, including OPA.

In this study, VAX-24 was well-tolerated and demonstrated a safety profile similar to PCV20 across all doses studied. Post-dose 3 and post-dose 4, all VAX-24 doses evaluated demonstrated robust IgG and OPA immunogenicity responses.

•Post-dose 3, all VAX-24 doses met target precedent Phase 2 non-inferiority criteria on relative seroconversion rates (lower limit of the 95% confidence interval for the difference between the proportion of participants achieving the pre-defined seroconversion rate (IgG concentration ≥0.35 mcg/mL) is > -15% for each serotype) for the highest circulating serotypes, as defined by the

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percentage of IPD caused in individuals <5 yrs of age in the U.S. in 2023 based on the U.S. Center for Disease Control ("CDC") active bacterial core ("ABC") surveillance data, contained in VAX-24. The Low and Mid doses met the seroconversion rate criteria for 20 of 24 serotypes overall and the Mixed Dose met such criteria for 19 of 24 serotypes. The Mid and Mixed Doses met the target Phase 2 IgG GMR point estimate of >0.6 for 21 of 24 serotypes.

•Post-dose 4, all VAX-24 doses met our target Phase 2 IgG GMR point estimate of >0.6 for the three highest circulating serotypes contained in VAX-24. The Mixed Dose met this target for 19 of 24 serotypes overall and the Mid dose met this target for 18 of 24 serotypes. Post-dose 4, VAX-24 elicited robust memory responses across all doses for all serotypes.

•Additionally, the four incremental serotypes unique to VAX-24 that provide expanded serotype coverage relative to PCV20 elicited robust immune responses and met all target criteria across all endpoints at all doses evaluated.

•The final positive data from the VAX-24 infant Phase 2 dose-finding study further validated our rationale for exploring higher doses in the ongoing VAX-31 infant Phase 2 study.

◦VAX-XL is a third-generation PCV candidate designed to provide the broadest coverage of any PCV currently in development.

•VAX-A1, a novel conjugate vaccine candidate designed to prevent disease caused by Group A Streptococcus (“Group A Strep”). Group A Strep is pervasive globally and causes an estimated 800 million cases of illness annually, including pharyngitis, or strep throat, and certain severe invasive infections and sequelae. There is currently no vaccine against Group A Strep, which is one of the leading infectious disease-related causes of death and disability worldwide and a significant contributor to the prescription of antibiotics in children. We believe we have demonstrated preclinical proof of concept for VAX-A1, the data for which were published in December 2020. We plan to initiate a Phase 1 adult study for VAX-A1 in 2026, with the primary objective of assessing safety and tolerability.

•VAX-GI, a novel preclinical vaccine candidate being developed as a preventative treatment for dysentery and shigellosis, which is caused by Shigella bacteria. Shigella is a bacterial illness estimated to cause 80 million to 165 million cases of disease and 600,000 deaths annually, mostly among children. The central antigen in VAX-GI is IpaB, a well-appreciated antigen that other developers have been unable to produce in an amount sufficient to enable a commercial product. With our cell-free technology, we believe we can produce this antigen at substantially improved yields, allowing for commercial-scale production. VAX-GI is being developed in collaboration with the University of Maryland, Baltimore as well as with partial funding from two research grants awarded by the National Institutes of Health (“NIH”). As part of our continued focus on strategic capital deployment and in order to prioritize our resources towards our PCV franchise, we announced in August 2025 that we had paused the advancement, beyond preclinical development, of VAX-GI while remaining confident in its potential and preserving the option to advance the program in the future.

•Other discovery-stage programs that leverage our cell-free protein synthesis platform, which, if proven successful in preclinical studies, could also be advanced into IND-enabling activities and clinical studies.

Our Approach

To address areas of significant unmet medical need, we carefully select the disease areas we target and are developing vaccine candidates based on the following criteria:

•Clear commercial opportunity and efficient market adoption: We select vaccine targets that are characterized by an established patient population and significant unmet medical need. Our PCV candidates are designed to improve upon the standard-of-care for both adults and children by covering the serotypes that are responsible for a significant portion of IPD in circulation and are associated with high case-fatality rates, antibiotic resistance and meningitis, while maintaining coverage of previously circulating strains that are currently contained through continued vaccination practice. We believe that by providing the broadest coverage of serotypes for PCVs, as well as providing novel vaccines for diseases for which there are no currently approved vaccines, we can leverage the

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U.S. Centers for Disease Control (“CDC”), ACIP and similar international advisory body recommendations to drive rapid and significant market adoption.

•Acceptable biological risk: We choose vaccine targets with well-understood mechanisms of action and strong precedents for positive preclinical study results that we believe will translate to positive clinical trial results. For example, conjugate vaccines have demonstrated effectiveness in both preclinical and clinical trials against a range of bacteria, including Streptococcus pneumoniae, meningococcus and haemophilus influenza B. There is consistent evidence that antibodies directed against these bacteria are protective against their respective diseases.

•Established or acceptable clinical pathways: We pursue vaccine targets that we believe have established or acceptable clinical development pathways in order to accelerate the potential time to market. For example, we believe that our PCVs would receive regulatory approval based on successful completion of clinical studies utilizing well-defined surrogate immune endpoints, consistent with how other PCVs have obtained regulatory approval in the past, rather than requiring clinical field efficacy studies. For our novel vaccine candidates, for which we believe clinical field efficacy studies will be necessary, we select disease areas with high attack rates, such as Group A Strep, which may allow for more manageable study sizes.

Our Platform

Our modern synthetic techniques, including advanced chemistry and the XpressCFTM cell-free protein synthesis platform, offer several advantages over conventional cell-based protein expression methods, which we believe enable us to generate superior, novel, broader-spectrum and/or more immunogenic vaccines. In the context of conjugate vaccines, we believe we can add more antigenic strains without compromising the overall immune response. In particular, our ability to specify the attachment point of antigens, including polysaccharides, on protein carriers represents a significant improvement over the random conjugation that occurs with conventional technologies. This site-specific conjugation is designed to ensure that B-cell and/or T-cell epitopes are optimally exposed, maximizing the immune response, whereas random conjugation blocks these critical immunogenic epitopes, which dampens the immune response and may lead to a phenomenon known as carrier suppression.

We believe this precise control of conjugation chemistry enables us to design broader-spectrum conjugate vaccine candidates using carrier-sparing conjugates that use less protein carrier without sacrificing immunogenicity. We are also able to design novel conjugate vaccine candidates using standard amounts of protein carrier to generate heightened immunogenicity. Beyond conjugate vaccines, we believe we can also design novel protein vaccine candidates based on well-appreciated but highly complex antigens that currently cannot be made using conventional technologies to address diseases for which there are no available vaccines. In addition, our platform enables us to rapidly screen vaccine candidates, requiring less effort than conventional chemistry which allows us to produce and iterate conjugate candidates, thereby dramatically accelerating the development cycle of designing, producing and testing vaccine candidates.

We are re-engineering the way highly complex vaccines are made to develop potentially superior and novel conjugate and protein vaccine candidates for adult and pediatric indications using the above criteria by taking advantage of the following:

•Site-specific conjugation. We are able to specify the attachment point of antigens, including polysaccharides, on protein carriers to ensure optimal exposure of B-cell and/or T-cell epitopes, thereby creating protein carriers designed to have enhanced potency. We believe this precise control of conjugation chemistry enables us to create broader-spectrum conjugate vaccine candidates using carrier-sparing conjugates that use less protein carrier without sacrificing immunogenicity. We are also able to design novel conjugate vaccine candidates using standard amounts of protein carrier to generate heightened immunogenicity.

•Production of novel protein vaccines. We can design novel protein vaccine candidates based on well-appreciated but highly complex antigens that currently cannot be made with conventional technologies to address diseases for which there are no available vaccines, and we believe we may be able to leverage our platform to rapidly respond to new or emerging pathogens. We can design and produce these “tough-to-make” antigens that conform to the target pathogens, thereby increasing the likelihood that the vaccine will elicit a protective immune response.

•Speed, flexibility and scalability of the discovery engine. We are able to rapidly screen vaccine candidates and produce conjugates, thereby accelerating the process of making and testing vaccine candidates. Because cell viability is not required for cell-free protein synthesis, we can utilize a broader range of reaction conditions as we seek to optimize proteins. This flexibility enables us to develop novel vaccine candidates unachievable with current technologies. Furthermore, we believe our platform can scale linearly from discovery to commercial scale.

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Our Strategy

Our goal is to become a leader in the vaccines industry by using our cell-free protein synthesis platform to develop superior and/or novel vaccines to prevent or treat serious infectious diseases. Key elements of our strategy include:

•Advance our PCV candidates through clinical development and regulatory approval. Our PCV candidates, VAX-31,VAX-24 and VAX-XL, target the pneumococcal vaccine market. We are advancing these PCV candidates along a well-understood clinical development pathway in an effort to obtain regulatory approval in adults and infants based on successful completion of clinical studies using previously established surrogate immune endpoints, without the need to conduct clinical field efficacy studies, consistent with how other conjugate vaccines have obtained approval.

•Establish scalable production of our PCV candidates. We believe high-quality and scalable manufacturing is critical to our long-term success. We have designed and developed a proprietary, scalable and portable manufacturing process that we have scaled to supply clinical volumes and believe can scale to supply initial volumes of VAX-31 needed to support commercial launch. We have access to substantial manufacturing resources through our contract manufacturer, Lonza, that we believe can facilitate an independent path to market. For the adult indication, we are conducting scale-up activities to support potential regulatory approval and commercial launch of VAX-31 in this population using existing Lonza infrastructure. In October 2023, to complement this plan, we entered into a new commercial manufacturing agreement with Lonza to support the potential global commercialization of our PCV candidates in both the adult and pediatric populations. In November 2023, we entered into a manufacturing rights agreement with Sutro Biopharma, Inc ("Sutro Biopharma") to obtain control over the development and manufacture of cell-free extract, a key component of our PCV franchise. Pursuant to the manufacturing rights agreement, we obtained exclusive rights to independently, or through certain third parties, develop, improve and manufacture cell-free extract for use in connection with our vaccine candidates. In addition, in September 2025, we announced a new agreement with Patheon Manufacturing Services, LLC, part of Thermo Fisher Scientific (collectively, "Thermo Fisher") to provide custom commercial fill-finish capacity for our broad-spectrum PCVs at Thermo Fisher's Greenville, North Carolina facility. The initiative, which includes both manufacturing and related services, represents a long-term U.S. commercial manufacturing commitment of up to $1 billion.

•Create a long-lasting PCV franchise by offering the broadest-spectrum PCV available. The two leading pneumococcal vaccine franchises to date, Prevnar and Pneumovax 23 (“PPSV23”), have been administered well over a billion times, generating over $100 billion in combined sales over 20 and 40 years, respectively, and can attribute their success to having been the broadest-spectrum vaccines on the market. In addition, the recently approved PCV, Capvaxive® ("PCV21"), is now commercially available for the adult market. If approved, we believe VAX-31 and/or VAX-24 may potentially replace the standard-of-care PCVs currently available because of their coverage against both currently circulating and historically prevalent strains. We designed VAX-24 to address the 24 pneumococcal strains covered by Prevnar and PPSV23 that drive a significant portion of pneumococcal disease today with the durable, boostable immune response of a conjugate vaccine. Further, we have designed VAX-31 to address these 24 strains plus seven additional epidemiologically significant emerging strains that are causing increasing pneumococcal disease and antibiotic resistance, which collectively drive most pneumococcal disease today. With these broad-spectrum vaccine candidates, we believe we are well-positioned to obtain ACIP recommendations and potentially replace the current standard-of-care for pneumococcal disease prevention in both adult and pediatric populations, thereby creating a long-lasting PCV franchise.

•Develop novel vaccine candidates and leverage our platform to expand our pipeline.

◦ VAX-A1: We believe our data published in December 2020 demonstrated preclinical proof of concept for VAX-A1. We nominated the final vaccine candidate and initiated IND-enabling activities for VAX-A1 in 2021. We plan to initiate a Phase 1 adult clinical study in 2026, with the primary objective of assessing safety and tolerability.

◦VAX-GI:VAX-GI is being developed in collaboration with the University of Maryland, Baltimore as well as with partial funding from two research grants awarded by the NIH. We are in the process of identifying additional antigens to include with IpaB and engaged in early-stage process development activities. As part of our continued focus on strategic capital deployment and in order to prioritize our resources towards our PCV franchise, we announced in August 2025 that we had paused the advancement, beyond preclinical development, of VAX-GI while remaining confident in its potential and preserving the option to advance the program in the future.

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◦Leverage our platform for other discovery stage programs. We are also able to leverage our platform as a discovery engine given our ability to uniquely create building blocks to construct potential novel conjugate and protein vaccine candidates, and we have other discovery-stage programs which leverage this platform.

•Continue to build a robust intellectual property portfolio. We have developed and are continuing to develop a comprehensive intellectual property portfolio related to vaccine applications, including manufacturing, formulation and process applications as well as protection for our specific vaccine candidates. We have rights to a robust portfolio of patents and patent applications related to the XpressCF platform through our exclusive license from Sutro Biopharma. We currently have four issued U.S. patents, two issued European patents and multiple issued patents internationally, and multiple pending patent applications in the United States and internationally that cover our vaccine candidates including vaccine formulations, protein-antigen conjugates, methods of making conjugate vaccines with various protein-antigen conjugates and other processes related to vaccine production, enhancements of immunogenicity and methods of use.

Our Pipeline

We have utilized our cell-free protein synthesis platform to generate a pipeline of vaccine candidates that we believe, if approved, may offer important advantages over existing vaccines or for which there are no vaccines available today. The following table summarizes our current pipeline:

Global Vaccine Market

The global vaccine market size is projected to reach $115.77 billion by 2033 from an estimated $72.75 billion in 2025, growing at a compounded annual growth rate of 5.78% from 2026 to 2033. The Prevnar franchise from Pfizer Inc. (“Pfizer”), comprised of Prevnar 13 (“PCV13”) and PCV20, was among the highest selling vaccine products in the world in 2025, accounting for an estimated 9% of global vaccine sales.

The pediatric vaccine market is large and well-established in the United States, European Union and many other countries around the world. The annual new birth cohort, which in North America and Europe approached approximately 10 million in 2024, drives ongoing sales year after year due to the recommended immunization schedules. In the United States, once a new vaccine is approved by the FDA, the ACIP considers whether to recommend the use of the vaccine. New pediatric vaccine classes that receive a recommendation from ACIP and/or government health and professional medical organizations are widely adopted by pediatricians and parents and are required by many schools, contributing to a national immunization rate for the diseases targeted by such vaccines of approximately 90%. It is estimated that vaccination in children born between 1994 and 2023 in the United States will result in net savings of $540 billion in direct costs and $2.7 trillion in societal costs, making them one of the most cost-effective public health interventions.

In addition, the adult vaccine market is undergoing rapid growth. Vaccination rates among adults have historically been lower relative to infants and vary by disease, though strong initiatives are underway to increase awareness and utilization.

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Excluding the impact of the COVID-19 pandemic, studies estimate that tens of thousands of adults in the United States die annually of vaccine-preventable diseases, and hundreds of thousands more are hospitalized. Vaccine-preventable diseases among adults cost the U.S. economy an estimated $27 billion annually in direct and indirect expenses. In recent years, manufacturers have started developing more vaccines for the adult market, including Pfizer’s PCV13 and PCV20, Merck & Co., Inc.'s (“Merck”) PCV15 and PCV21, GSK plc's (“GSK”) Shingrix and multiple vaccines to prevent respiratory syncytial virus ("RSV"). The U.S. adult pneumococcal market generated estimated annual sales of more than $1.5 billion in 2025, and Shingrix, a vaccine for shingles (herpes zoster), debuted with over $1 billion in sales in 2018 as it replaced Merck’s incumbent vaccine, Zostavax, after receiving an ACIP preferred recommendation, and generated over $4.8 billion in global sales in 2025. The vaccines to prevent RSV from Pfizer and GSK that were approved by the FDA in May 2023, and from Moderna that was approved by the FDA in May 2024, generated approximately $1.8 billion in global sales in 2025.

In October 2024, the ACIP voted to recommend expanding the age-based pneumococcal vaccination guidelines for pneumococcal vaccination in adults to begin at 50 years of age and older from the prior recommendation beginning at 65 years of age and older, which expanded the market by adding approximately 62 million additional eligible Americans for the universal recommendation.

Pneumococcal Disease

Pneumococcal disease is an infection caused by Streptococcus pneumoniae bacteria. It can result in IPD, including meningitis and bacteremia, and non-invasive pneumococcal disease, including pneumonia, otitis media and sinusitis. Global pneumococcal disease in children is driven by emerging serotypes not covered by currently available vaccines and in adults by not only emerging serotypes, but also fragmented coverage of today's standard-of-care vaccines. In the United States, pneumococcal pneumonia is estimated to result in approximately 225,000 U.S. adult hospitalizations each year. Streptococcus pneumoniae is among the WHO’s top antibiotic-resistant pathogens to be urgently addressed, and the United States CDC lists drug-resistant Streptococcus pneumoniae as a “serious threat.” In children under five, Streptococcus pneumoniae is the leading cause of vaccine-preventable deaths globally, resulting in approximately 300,000 deaths annually. It is estimated that acute otitis media affects approximately 5 million children and results in greater than 10 million antibiotic prescriptions annually in the United States. Pneumococci also cause over 50% of all cases of bacterial meningitis in the United States. Antibiotics are used to treat pneumococcal disease, but some strains of the bacteria have developed resistance to treatments. The morbidity and mortality due to pneumococcal disease are significant, particularly for young children and older adults, underscoring the need for a broader-spectrum vaccine.

Evolution of Pneumococcal Vaccines

There are currently two types of vaccines targeting pneumococcal disease—polysaccharide-only vaccines and PCVs. Polysaccharide vaccines contain polysaccharide antigens, which induce antibodies (B-cell responses) that bind to a bacteria’s outer coating of polysaccharides and clear the bacteria. PCVs improve on polysaccharide vaccines by attaching, or conjugating, the polysaccharide antigen to a non-disease specific protein carrier. PCVs induce both an improved B-cell response and a T-cell response, resulting in a stronger and more durable immune response and longer-lasting protection, as compared to polysaccharide vaccines, which only induce a B-cell response.

Pneumococcal Polysaccharide-Only Vaccines

PPSV23, manufactured and marketed by Merck is the only pneumococcal polysaccharide vaccine widely available. PPSV23 is indicated for the prevention of pneumococcal disease in adults and was first approved in the United States in 1977, at which time it contained 14 different strains of pneumococcal bacteria. In 1983, it was replaced by the current version containing 23 different strains. PPSV23 is routinely administered to adults to provide protection against bacteremia and at its peak in 2020 generated sales of over $1.1 billion. After the ACIP recommendation of PCV20 in late 2021 eliminated the need for PPSV23 in a large part of the covered population, PPSV23 has declined from more than 50% of the U.S. adult market share to less than 3%.

Polysaccharide vaccines induce a B-cell response only and do not induce a T-cell dependent immune response. In the absence of immunological memory responses, the resulting antibody responses are transient and cannot be boosted. Without the ability to provide long-lasting durable immunity, polysaccharide vaccines are not effective in children below two years of age. In addition, the antibody responses primarily consist of immunoglobulin M (“IgM”) antibodies that, due to their size, are restricted to blood and are unable to penetrate into lung tissue to protect against pneumonia. Therefore, polysaccharide vaccines such as PPSV23 are only thought to protect against blood-borne infections, such as bacteremia. Figure 1 below illustrates polysaccharide-induced T-cell independent antibody responses.

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Figure 1.

Graphics adapted from Strugnell et al, Understanding Modern Vaccines, Vol 1, Issue 1, 61-88.

Polysaccharide vaccines also interfere with optimal use of PCVs, as they create a hyporesponsive immune effect. In particular, absent T-cell inducement, polysaccharide vaccines actually clear the memory B-cells that are formed following primary immunization with a PCV, thereby eliminating the ability to boost with subsequent vaccination. This historically has been a significant drawback of vaccination in older adults, which consisted of the administration of a limited spectrum PCV followed by the administration of a polysaccharide vaccine. Despite these shortcomings, PPSV23 historically has been widely used primarily to provide protection against circulating strains not contained in the currently available PCVs. The current routine standard-of-care in adults, which consists of the administration of either PCV20 or PCV21 alone or PCV15 followed by the administration of PPSV23, continues to include the alternative of a polysaccharide vaccine.

Pneumococcal Conjugate Vaccines

PCVs overcome the limitations of polysaccharide vaccines by conjugating the polysaccharide to a more immunogenic protein carrier containing T-cell epitopes. These T-cell epitopes provide CD4+ help, which is critical to the conversion of a traditional B-cell dependent immune response to a more robust combined B-cell and T-cell dependent immune response. The T-cell response causes immediate class switching of the B-cells from more rudimentary IgM antibodies prevalent with polysaccharide vaccines to more refined IgG antibodies. IgG antibodies are refined enough to penetrate into lung tissues to prevent pneumonia. Furthermore, as polysaccharide strands attach to multiple copies of the protein carrier, they create an inter-strand cross-linked matrix structure, which the immune system easily recognizes as foreign. The T-cell dependent immune response also generates memory B-cells that can be re-stimulated, creating a prime-boost immune response leading to a more robust and durable immune response and enabling the use of PCVs in young children. Figure 2 below illustrates this immune response:

Figure 2.

The first PCV, Prevnar, was a 7-valent vaccine that was launched in the United States in 2000. It included purified capsular polysaccharides of seven serotypes of Streptococcus pneumoniae (4, 6B, 9V, 14, 18C, 19F and 23F), each of which was individually conjugated to a T-cell-epitope-containing, nontoxic variant of diphtheria toxin known as CRM197 to produce

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seven separate conjugates. To obtain approval, a large field efficacy study was conducted that demonstrated the vaccine’s efficacy in infants. Efficacy correlated with serological immune endpoints, as measured by IgG titers (a measurement of concentration), and a seroconversion threshold (or reference antibody concentration) of protection was defined. Prevnar is credited with tremendous medical and commercial success, having dramatically reduced circulating disease in children. However, after a number of years of widespread use, IPD incidence caused by strains not contained in the vaccine started to opportunistically rise, a phenomenon called serotype replacement, which led to the need for a broader-spectrum version of the vaccine.

In the race to develop a broader-spectrum PCV than Prevnar, two vaccines were successfully developed: Synflorix, a 10-valent PCV from GSK, and PCV13, a 13-valent PCV from Wyeth (subsequently acquired by Pfizer). Based on its broader coverage of then-emerging strains, PCV13 was adopted as the standard-of-care in the United States and Europe. Synflorix's use has been limited primarily to emerging countries.

PCV13 contains the seven serotypes originally included in Prevnar plus six more serotypes of Streptococcus pneumoniae (1, 3, 5, 6A, 7F and 19A) and was approved and launched in the United States in 2010. Each polysaccharide is conjugated to CRM197 to produce 13 individual conjugates, which are mixed into a final vaccine formulation and then adsorbed to alum. In 2010, PCV13 obtained FDA approval for the prevention of IPD in infants based on non-inferior IgG antibody responses relative to Prevnar, using the surrogate immune endpoints established by the prior Prevnar field efficacy study. While PCV13 failed to achieve non-inferiority on two of the common seven strains relative to Prevnar, it was granted approval across all 13 strains. Upon receipt of the ACIP recommendation, PCV13 replaced Prevnar in the infant market as the standard-of-care. This also created a “catch-up” population for those children previously vaccinated with Prevnar to provide protection against the incremental serotypes covered by PCV13.

In an effort to develop even broader-spectrum PCVs than PCV13, two vaccines were successfully developed for the adult and infant populations: PCV20, a 20-valent PCV from Pfizer, and PCV15, a 15-valent PCV from Merck.

PCV20 contains the 13 serotypes included in PCV13 plus seven more serotypes of Streptococcus pneumoniae (8, 10A, 11A, 12F, 15B, 22F and 33F) and was granted regulatory approval and launched in the United States in 2021 for the prevention of IPD and pneumonia in adults based on non-inferior OPA responses relative to PCV13 without the need for a field efficacy study. PCV20’s indication for the prevention of pneumonia caused by Streptococcus pneumoniae serotypes 8, 10A, 11A, 12F, 15B, 22F, and 33F in adults is approved under accelerated approval based on immune responses as measured by OPA assay. While PCV20 failed to achieve non-inferiority on serotype 8 relative to PPSV23, it was still granted approval across all 20 strains. In 2023, the FDA approved PCV20 for use in infants for the prevention of IPD, and for the prevention of otitis media caused by Streptococcus pneumoniae serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F without the need for a field efficacy study. While PCV20 failed to achieve non-inferiority for five of the 13 common (1, 3, 4, 9V and 23F) and one of the seven unique (12F) serotypes for the co-primary endpoint following the three-dose primary immunization series in the U.S. study, it was still granted FDA approval across all 20 strains for IPD.

PCV15 contains the 13 serotypes included in PCV13 plus two more serotypes of Streptococcus pneumoniae (22F and 33F) and was granted regulatory approval and launched in the United States in 2021 for the prevention of IPD in adults based on non-inferior OPA responses relative to PCV13 without the need for a field efficacy study. In 2022, the FDA approved PCV15 for use in infants for the prevention of IPD based on non-inferior IgG responses relative to PCV13 without the need for a field efficacy study.

In October 2021, the ACIP voted to recommend universal vaccination for the use of either PCV20 alone or PCV15 with PPSV23 for routine use in adults aged 65 years and older as well as for those between the ages of 19 and 64 years with certain underlying medical conditions or other risk factors who had not previously received a PCV or whose previous vaccination history was unknown. In June 2022, the ACIP voted to recommend that PCV15 may be used as an option to the then recommended PCV13 for children aged under 19 years according to then recommended PCV13 dosing and schedules. In October 2022, the ACIP voted to recommend a dose of PCV20 for adults aged 65 years and older at least five years after the last pneumococcal vaccine dose for those who haven't previously received PCV20. In June 2023, the ACIP voted to recommend the use of PCV20 as an option to PCV15 for routine use in children under the age of two, and as a “catch up” vaccination for healthy children between the ages of 24 and 59 months with incomplete PCV vaccination status and children between the ages of 24 and 71 months with certain underlying conditions and an incomplete PCV vaccination status. Further, the ACIP voted to recommend that children between the ages of two and 18 years with any risk condition who have received all recommended PCV doses before the age of six do not need additional doses if they have received at least one dose of PCV20. If children between the ages of two and 18 years with any risk condition received PCV13 or PCV15, but not PCV20, the ACIP recommended that they should receive a dose of PCV20 or PPSV23. The ACIP also voted to recommend that children between the ages of six and 18 years with any risk condition who have not received any dose of PCV13, PCV15 or PCV20 should receive a single dose of PCV15 or PCV20. When PCV15 is used in this instance, the ACIP recommended that it should be followed by a dose of PPSV23 at least eight weeks later if not previously given.

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In June 2023, the ACIP also recommended shared clinical decision-making regarding PCV20 use for adults aged 65 years and older who have completed the recommended vaccine series with both PCV13 and PPSV23.

As a further example of the need for broader-protection vaccines to prevent IPD highlighted by the public health community, another vaccine was successfully developed for the adult population: PCV21, a 21-valent PCV from Merck. Unlike predecessor PCVs, PCV21 does not contain each of the historically circulating serotypes covered in previously approved PCVs. PCV21 contains 11 of the 20 serotypes included in PCV20 (serotypes 3, 6A, 7F, 8, 10A, 11A, 12F, 15B, 19A, 22F and 33F) plus 10 more serotypes of Streptococcus pneumoniae (serotypes 9N, 15A, 16F, 17F, 20, 23A, 23B, 24F, 31 and 35B). PCV21 was granted regulatory approval and launched in the United States in 2024 for the prevention of IPD and pneumonia (serotypes 3, 6A, 7F, 8, 9N, 10A, 11A, 12F, 15A, 15C, 16F, 17F, 19A, 20A, 22F, 23A, 23B, 24F, 31, 33F, and 35B) in adults based on non-inferior OPA responses relative to PCV20 without the need for a field efficacy study. PCV21’s indication for the prevention of pneumonia is approved under accelerated approval based on immune responses as measured by OPA.

In June 2024, the ACIP voted to recommend PCV21 as an option to either PCV20, or PCV15 with PPSV23, for (i) adults aged 65 years and older who have not previously received a PCV or whose previous vaccination history is unknown, (ii) adults between the ages of 19 and 64 with certain underlying medical conditions or other risk factors who have not previously received a PCV or whose previous vaccination history is unknown and (iii) adults aged 19 years and older who have received PCV13 but not all recommended doses of PPSV23. Additionally, the ACIP recommended shared clinical decision-making regarding a supplemental dose of PCV21 for adults aged 65 and older who have completed their vaccine series with both PCV13 and PPSV23.

In October 2024, the ACIP expanded its recommendation by lowering the age-based pneumococcal vaccination guidelines for pneumococcal vaccination in adults from 65 years and older to 50 years and older. In line with this recommendation, the ACIP recommends either a dose of PCV20 or PCV21, or PCV15 with PPSV23, for (i) adults aged 50 and older who have not previously received a PCV or whose previous vaccination history is unknown and (ii) adults between the ages of 19 and 49 with certain underlying medical conditions or other risk factors who have not previously received a PCV or whose previous vaccination history is unknown.

Drawbacks of Current PCVs

Routine immunization with PCVs has been effective in dramatically lowering the incidence of IPD in both adults and children in the United States and other industrialized nations. However, due to a phenomenon called serotype replacement, strains that are not covered by existing vaccines are increasing in prevalence. As published in 2022, 35% and 37% of IPD incidence in 2018 for children under the age of five and adults aged 65 years and older, respectively, were caused by strains beyond the 20 strains covered by PCV20. Efforts to improve upon standard-of-care vaccines center around expanding the valency of PCVs to address the strains driving residual pneumococcal disease. However, limitations due to conventional conjugation chemistry and carrier suppression have complicated those efforts, and notwithstanding the recent approvals of PCV21 in adults, PCV20 and PCV15, there remains a significant need for broader-spectrum PCVs that address both currently circulating and historically prevalent serotypes, as evidenced by the fact that despite the coverage of PCV21 and PCV20, the combination of PCV15 and PPSV23 remains universally recommended when adults turn 50 in the United States, as an alternative to either PCV21 or PCV20 alone, given the broader-spectrum coverage of these two vaccines combined compared to PCV21 or PCV20. Although PCV21 covers more incidence of disease, it does not address several of the serotypes historically covered, many of which continue to circulate today.

While vaccination with current PCVs has been effective in dramatically lowering the incidence of IPD in both adults and children in the United States and other industrialized nations, current PCVs suffer from the following drawbacks.

Serotype Replacement

Since the introduction of PCV13, there has been a decrease in incidence of disease attributable to the serotypes included in the vaccine. However there has been a phenomenon called serotype replacement, whereby a void is created when serotypes are taken out of circulation after widespread vaccination. As a result, serotypes not covered by PCV13 now cause residual pneumococcal disease. Broader-spectrum PCVs were historically required to maintain protection against historically pathogenic strains while expanding coverage to address current circulating and emerging strains. This serotype replacement has led to the development of a third generation of conventional PCVs, inclusive of PCV15 and PCV20. Although PCV21 was approved despite lacking protection against certain historically pathogenic strains, it is only approved in the adult population and did not receive a preferred recommendation despite its disease coverage, and is recommended solely as an alternative to PCV20 alone or PCV15 and PPSV23. VAX-31, if approved, would increase coverage to more than 95% of IPD currently circulating in the U.S. adult population aged 50 and over. In the pediatric population, VAX-31 is designed to cover approximately 92% of IPD in U.S. children under five years of age and approximately 96% of otitis media due to Streptococcus pneumoniae in U.S. children five years of age or under.

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Pneumococcal disease surveillance has been conducted by the CDC in the United States and by the UK Health Security Agency. As shown in Figure 3, IPD cases in adults in the United States initially declined after the introduction of PCV13 but have since plateaued. The rate of serotype replacement has been more pronounced in the United Kingdom. Figure 4 shows the approximate IPD incidence rates in the United Kingdom caused by the incremental strains over and above those in PCV13, which increased over the last three years of surveillance.

Figure 3. Figure 4.

While some of these strains are covered by PPSV23, that vaccine only protects against blood-borne infections and not pneumonia, leaving patients vulnerable to infection. Although PCV21, PCV20 and PCV15 address more disease-causing strains than PCV13, we believe there remains a significant need for even broader-spectrum vaccines to address a greater number of currently circulating and emerging strains.

Carrier Suppression

Technical constraints inherent to conventional conjugation chemistry limit the coverage of current PCVs due to a phenomenon known as carrier suppression. In particular, traditional conjugation methods cannot control where conjugation of the polysaccharide occurs on the protein carrier. The protein carrier used in all versions of Prevnar is CRM197, a diphtheria toxin with a single point mutation rendering it non-toxic. The CRM197 protein contains 39 lysines, approximately 20% of which border relevant T-cell epitopes. Conventional conjugation chemistry randomly attaches the polysaccharide to any of the numerous lysines located on the protein carrier. When a polysaccharide is covalently bound to a protein carrier at a lysine residue that is co-resident with a T-cell epitope, it blocks the presentation of the T-cell epitope to the immune system, thus preventing the induction of a T-cell response. The masking of these critical epitopes prevents the conversion to a T-cell dependent immune response and negates the benefit of the protein carrier.

Meanwhile, the B-cell epitopes of both the protein carrier and the antigen are presented to the immune system, causing B-cells to the respective immunogens to compete with one another for the T-cell help engendered by unblocked T-cell epitopes. This competition for T-cell helps diminish the immune response to the polysaccharide antigen of interest, resulting in carrier suppression.

The result of carrier suppression is a decrease in the targeted immune response to the disease-specific polysaccharides, which intensifies with higher cumulative amounts of protein carrier. This phenomenon impedes the ability to expand coverage of current PCVs and has been shown consistently when broader-spectrum versions of conventional PCVs have been compared to lesser-valent versions. When PCV20 was compared to PCV13 in a well-controlled Phase 3 study in infants, the IgG antibody responses directed against the polysaccharides of interest for all thirteen of the common strains in each vaccine were lower for PCV20 (Figure 5). In 2020, Pfizer presented results of a well-controlled Phase 3 study in adults, aged 60 and over, where they compared PCV20 to PCV13. In that study, the OPA responses directed against the polysaccharides of interest for all thirteen of the common strains were lower for PCV20 (Figure 6).

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Figure 5. Figure 6.

1 IgG Geometric Mean Concentrations post-dose 4 – Prevnar 20 Biologics License Application ("BLA") Clinical Review Memorandum by FDA (STN: 125731/189). April 27, 2023.

2 PCV20 BLA Clinical Review Memorandum. STN: 125731/0 June 8, 2021.

Conventional Chemistry

The problem of carrier suppression is compounded by conventional conjugation chemistry used to make current PCVs, including PCV15, PCV20 and PCV21, which requires a higher amount of CRM197 protein carrier than polysaccharide antigen to complete the conjugation reaction, as well as long reaction times and harsh conditions that can damage the critical epitopes on the polysaccharide antigens. This results in a higher ratio of protein carrier to polysaccharide antigen in their monovalent conjugates (approximately 1.1 on average), as well as a much higher amount of cumulative protein carrier in the final formulation compared to the amount of any given polysaccharide antigen. For example, in the marketed PCV20 formulation, there are 51 micrograms of the protein carrier, CRM197, relative to 2.2 micrograms of each polysaccharide (except serotype 6B at 4.4 micrograms), and in the marketed PCV21 formulation, there are 65 micrograms of CRM197, relative to 4.0 micrograms of each polysaccharide. With substantially more protein carrier in the vaccines than polysaccharide antigen, the carrier suppression effect discussed above is exacerbated.

Our Solution

We are leveraging our cell-free protein synthesis platform to develop potentially superior conjugate vaccines for adult and pediatric indications. Our solution to the drawbacks with conventional conjugate vaccine techniques represents the first of three main applications of our platform.

Platform Application One: Creating Superior Conjugate Vaccines

Using our cell-free protein synthesis platform, we are developing superior, novel carrier-sparing PCVs designed to have broader-spectrum coverage in an effort to address historic, current and future residual disease in ways that conventional technologies cannot. We are able to design our investigational PCVs using site-specific conjugation in an effort to ensure optimal exposure of targeted immunogenic T-cell epitopes on protein carriers. This enables us to create broader-spectrum conjugate vaccine candidates using carrier-sparing conjugates designed to minimize carrier suppression while maintaining protective immunogenicity.

Synthesizing proteins outside of a living host cell provides us greater freedom to design and produce specific proteins of interest under optimized conditions. We separate the precise cellular machinery required for transcription, translation and energy production—the critical components for protein production—into an Escherichia coli ("E. coli")-derived extract. We can then optimally express a single protein carrier by adding the plasmid-DNA encoding that protein into the extract mixture.

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Site-Specific Conjugation

Within a protein carrier, we can substitute non-native amino acids (“nnAAs”) for native amino acids at specific sites. These inserted nnAAs serve as conjugation anchors that permit the attachment of antigens, including polysaccharides, at a specific site on a protein carrier to ensure optimal exposure of B-cell and/or T-cell epitopes to induce the desired immune response. This precise site-specific linkage is not possible using conventional conjugation chemistry with conventional carrier proteins and affords an advantage to our conjugate vaccine candidates. Figure 7 below depicts our method of inserting nnAAs into a protein carrier, where the DNA sequence has been modified to permit nnAA incorporation into the protein at pre-selected sites using a nnAA-RNA permitting transcription and translation of the protein in the ribosome to yield the protein carrier with nnAAs site-specifically incorporated, facilitating site-specific conjugation.

Figure 7.

Most conjugate vaccines available today use a non-disease-specific protein carrier, CRM197, in order to leverage T-cell epitopes to induce a T-cell dependent immune response. This traditional method produces a heterogeneous mixture of conjugates with blocked and unblocked T-cell epitopes in a large immunogenic cross-linked matrix structure. In contrast, the precision and flexibility of cell-free protein expression, together with our ability to insert nnAAs, allow us to construct our proprietary enhanced protein carrier (“eCRM”) with pre-determined conjugation sites. Our method produces more homogenous conjugates that provide for the consistent exposure of T-cell epitopes and likewise form a large, immunogenic cross-linked matrix structure. By precisely conjugating polysaccharides to eCRM in a way that provides for optimal exposure of T-cell epitopes to the immune system, we can heighten immunogenicity attainable with conjugate vaccines.

The figures below illustrate the site-specific conjugation process. Figure 8 shows site-specific conjugation of the polysaccharide to the protein carrier, avoiding the T-cell epitopes. Figure 9 shows the inter-strand cross-linked matrix, which is the structure of each monovalent conjugate included in the final vaccine.

Figure 8. Figure 9.

We believe consistent exposure of T-cell epitopes should translate to higher potency of the protein carrier on a weight-to-weight basis. To harness this potential potency advantage, we have elected to construct conjugates with a lower ratio of protein carrier to polysaccharide than conventional PCVs. Our clinical studies to date validated our carrier-sparing approach to develop broader-spectrum PCVs. As a result, we believe we can incorporate more monovalent conjugates to

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create an even more broad-spectrum vaccine with less protein carrier per conjugate in order to minimize carrier suppression.

Better Chemistry

We also employ a rapid and less harsh chemistry method called copper-free click chemistry to site-specifically conjugate the polysaccharides to eCRM. We believe this distinctive technique is a better controlled, more efficient and faster method of conjugation relative to conventional chemistry used to make traditional PCVs. The click chemistry conjugation reaction is designed to cause less damage to the critical immunogenic epitopes on the protein carrier or the target antigen.

Our PCV Franchise

We are developing broad-spectrum investigational PCVs designed to improve serotype coverage compared to current standard-of-care PCVs and minimize carrier suppression. We currently have three PCV candidates in our differentiated PCV franchise: VAX-31, a 31-valent, broad-spectrum, carrier-sparing investigational PCV, which we are developing for both the infant and adult populations, VAX-24, a 24-valent, broad-spectrum, carrier-sparing investigational PCV for which we have completed a Phase 2 trial in both the adult and infant populations, and VAX-XL, a third-generation PCV candidate designed to provide the broadest coverage of any PCV currently in development. VAX-31, the broadest-spectrum PCV in the clinic, is designed to provide protection against both currently circulating and historically prevalent serotypes and cover approximately 95% and 92% of IPD circulating in the U.S. adult (ages 50 and older) and infant (under the age of five) populations, respectively. The 31 serotypes included in VAX-31 are associated with high case-fatality rates, antibiotic resistance and meningitis. VAX-24 covers more serotypes than any pneumococcal infant vaccine on the market today.

As shown in Figure 10 below, there are critical differences between VAX-31 and VAX-24 and other currently available PCVs relating to the protein carrier, particularly the use of site-specific conjugation and the milder reaction conditions. We achieve site-specific conjugation through the insertion of multiple nnAAs, which is not possible with the conventional chemistry used for making other PCVs. The click chemistry we use for site-specific conjugation may also minimize damage to the critical immunogenic epitopes on the protein carrier and the polysaccharides through milder and shorter reactions, while other PCVs use conventional chemistries that involve harsher and longer reaction conditions.

Figure 10.

Furthermore, VAX-31 and VAX-24 improve upon the serotype spectrum of coverage relative to PCV15 and PCV20 in both the adult and infant populations, and VAX-31 improves on the same in the adult population relative to PVC21, and use less protein carrier per conjugate than these conventional chemistry PCVs. In aggregate, VAX-31 contains more protein carrier, and VAX-24 contains a similar amount of protein carrier, relative to PCV15 and PCV20. We believe the resulting decreased carrier burden per conjugate of VAX-31 and VAX-24 are critical for minimizing carrier suppression and producing broader-spectrum pneumococcal vaccines without sacrificing immunogenicity.

Where appropriate, we capitalize on the efficiencies of well-established clinical, manufacturing and regulatory precedents by leveraging conventional methods for the development of our PCV candidates. For example, our polysaccharide antigens are primarily made using conventional fermentation and purification techniques and activated through conventional methods. They are also labeled through conventional amination methods prior to being conjugated to eCRM. In addition, we use the same critical quality attribute assays for molecular weight and free polysaccharide that have served as the

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physicochemical measures of conjugates and also serve as predictors of their immunogenicity in vivo. We also use conventional IgG and OPA serological assays to gauge the immunogenicity of our conjugates, which have served as surrogate immunological endpoints in clinical studies that enabled the approval of PCV13, PCV15, PCV20 and PCV21.

We are pursuing a well-characterized clinical development path for our PCV candidates, consistent with other PCV developers. We have been able to conduct smaller and shorter clinical trials that target immune endpoints (e.g., OPA and IgG responses) previously recognized by regulatory authorities, and anticipate that we will be able to conduct such studies going forward. Pfizer applied this approach to the development of PCV13 and PCV20 and Merck applied it to the development of PCV15 and PCV21. Based on this standard, as a prerequisite for regulatory approval, we believe that any investigational PCV will have to be compared to the standard-of-care at the time a clinical trial is initiated. Currently, the standard-of-care for routine use is either PCV20 or PCV21 alone or PCV15 followed by PPSV23 in adults and PCV20 or PCV15 in infants.

Clinical Development Overview

We are pursuing clinical development for adults with VAX-31 and, for the pediatric population, have completed a Phase 2 study with VAX-24 and are currently conducting a Phase 2 study with VAX-31.

Adult Indication

We have selected VAX-31 to advance to an adult Phase 3 program, which was initiated in December 2025.

For VAX-31, we achieved clinical proof of concept in September 2024 when we announced positive topline results from a Phase 1/2 study evaluating the safety, tolerability and immunogenicity of VAX-31 in healthy adults aged 50 and older. Based on these positive results, we selected the High Dose of VAX-31 to advance to an adult Phase 3 program. Following an FDA End-of-Phase 2 meeting, we initiated a Phase 3 pivotal, non-inferiority study in December 2025 and expect to announce topline safety, tolerability and immunogenicity data in the fourth quarter of 2026. In January 2026, we announced the initiation of an additional Phase 3 trial evaluating VAX-31 when administered concomitantly with a licensed, high-dose seasonal influenza vaccine in pneumococcal-naïve adults aged 50 years and older (“OPUS-2”). In February 2026, we announced the initiation of a separate Phase 3 study evaluating VAX-31 in adults previously vaccinated with lower-valency pneumococcal vaccines (“OPUS-3”). We expect to report safety, tolerability and immunogenicity data from the OPUS-2 and OPUS-3 studies in the first half of 2027. We are also planning for a manufacturing consistency study (e.g. a lot-to-lot study). Subject to the results of the adult Phase 3 studies, we would expect to submit a BLA shortly following the completion of the last Phase 3 study.

For adults, the FDA has granted VAX-31 BTD for the prevention of IPD as well as pneumonia caused by Streptococcus pneumoniae. A BTD is designed to expedite the development and review of drugs that are intended to treat serious or life-threatening conditions and is based upon preliminary clinical evidence indicating that the drug or vaccine may demonstrate substantial improvement over available therapies on one or more clinically significant endpoints.

Infant Indication

We have completed a Phase 2 study with VAX-24 and and are currently conducting a Phase 2 study with VAX-31 for the prevention of IPD in infants.

In March 2025, we announced positive topline, interim data from the VAX-24 infant Phase 2 study, a randomized, observer-blind, dose-finding two-stage clinical study evaluating the safety, tolerability and immunogenicity of VAX-24 in healthy infants that enrolled 803 participants.

In November 2025, we announced final safety, tolerability, and immunogenicity results from the VAX-24 infant Phase 2 study that were consistent with the positive interim data reported in March 2025 and showed that VAX-24 elicited robust, dose-dependent immune responses, with little to no evidence of carrier suppression observed.

In this study, VAX-24 was well-tolerated and demonstrated a safety profile similar to PCV20 across all doses studied. The results from this study informed advancement of our modified VAX-31 infant Phase 2 dose-finding study. The final positive data from the VAX-24 infant Phase 2 dose-finding study further validated our rationale for exploring higher doses in the ongoing VAX-31 infant Phase 2 study.

For VAX-31, in December 2024 we announced that the first participants were dosed in the first stage of a Phase 2 randomized, dose-finding study of VAX-31 in healthy infants, and in February 2025, we announced that the ongoing study

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had advanced to the second stage of the study and that the first participants had been dosed. In September 2025, we announced advancement of the modified VAX-31 infant Phase 2 randomized, dose-finding study to the third and final stage. The study advanced to the third and final stage following modifications to the protocol to add a new dose arm to evaluate the VAX-31 Optimized Dose (majority of serotypes dosed at 4.4mcg and the balance dosed at 3.3mcg) and discontinue enrollment in the Low Dose arm. The Middle and High Dose arms are continuing as planned. In January 2026, we announced that we had completed enrollment of this study.

Clinical Data: Adult Indication

We are using OPA titers as the primary immunogenicity endpoint for the VAX-31 program in adults. OPA is believed to be the primary protective mechanism against pneumococcal disease. In addition, we are measuring IgG responses as a secondary endpoint, as such responses may serve as supportive evidence of immunogenicity for comparison. We believe that these endpoints, if met in a Phase 3 trial, will be sufficient to obtain regulatory approval of VAX-31 and that we will not need a clinical field efficacy study.

The FDA has previously approved pneumococcal vaccines upon the establishment of non-inferiority based on a head-to-head comparison using established surrogate immune endpoints in the target population. For adults, PCV13 was approved based on the establishment of non-inferiority of OPA responses relative to PPSV23, on a strain-by-strain basis, where non-inferiority was defined as greater than or equal to 0.50 of the lower limit of the two-sided 95% confidence interval of the OPA geometric mean titer ratio. PCV20 was approved based on the same non-inferiority criterion but compared with PCV13 and PPSV23, while PCV15 was approved based on the same non-inferiority for the common serotypes, but a different non-inferiority criterion for the incremental strains compared to PCV13. PCV21 was approved based on the same non-inferiority criterion as PCV15, but compared to PCV20.

The VAX-31 Phase 1/2 clinical study was a randomized, observer-blind, active-controlled, dose-finding clinical study designed to evaluate the safety, tolerability and immunogenicity of VAX-31 at three dose levels (Low, Middle and High) and compared to PCV20 in 1,015 healthy adults aged 50 and older. In the Low, Middle and High Doses, all serotypes were dosed at 1.1mcg, 2.2mcg and 3.3mcg, respectively, except serotypes 1, 5 and 22F, which were dosed at 1.65mcg, 3.3mcg, and 4.4mcg, respectively. The Phase 1 portion of the study evaluated the safety and tolerability of a single injection of VAX-31 at three dose levels and compared to PCV20 in 64 healthy adults 50 to 64 years of age. In January 2024, we announced that the first participants were dosed in the Phase 2 portion of the Phase 1/2 study of VAX-31 in healthy adults. The initiation of the Phase 2 portion occurred after an independent Data Monitoring Committee conducted an assessment of the Phase 1 safety and tolerability results and recommended that the study proceed as planned to Phase 2. Phase 1 participants were evaluated for immunogenicity, and the Phase 1 safety, tolerability and immunogenicity data was pooled with the participants in the Phase 2 portion of the study. The Phase 2 portion of the study evaluated the safety, tolerability and immunogenicity of a single injection of VAX-31 at the same three dose levels and compared to PCV20, in 951 healthy adults 50 years of age and older. Participants were randomized equally in four separate arms and, 30 days after dosing, serology samples were collected to assess immunogenicity. The immunogenicity objectives of the study included an assessment of the induction of antibody responses, using OPA and IgG at each of the three VAX-31 doses and compared to PCV20, for the 20 serotypes in common, as well as for the additional 11 serotypes contained in VAX-31, but not in PCV20. Participants in the study were evaluated for safety through six months after vaccination. The study was conducted at approximately 25 sites in the United States. In January 2024, we announced the completion of enrollment in the Phase 1/2 clinical study evaluating VAX-31 in healthy adults aged 50 and older.

Figure 12 is a schematic of the overall study design of our VAX-31 adult Phase 1/2 study:

Figure 12.

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In September 2024, we announced positive topline results from the study.

Safety and Tolerability Findings:

As shown in Figure 13, based on the full six-month safety data, VAX-31 was observed to be well tolerated and demonstrated a safety profile at all doses studied through the full six-month evaluation period similar to PCV20. As shown in Figure 14 and Figure 15, frequently reported local and systemic reactions were generally mild-to-moderate, resolving within several days of vaccination, with no meaningful differences observed across the cohorts. No serious adverse events were considered to be related to study vaccines.

Figure 13.

Figure 14. Figure 15.

Immunogenicity Findings:

As shown in Figures 16 and 17, VAX-31 showed robust OPA immune responses for all 31 serotypes at all doses studied. At the Middle and High Doses, VAX-31 met or exceeded the regulatory immunogenicity criteria for all 31 serotypes and, at the Low Dose, for 29 of 31 serotypes.

As shown in Figure 16, at the Middle and High doses, VAX-31 met or exceeded the OPA response non-inferiority criteria (lower bound of the 2-sided 95% confidence interval of the OPA GMR is greater than 0.5) for all 20 serotypes common with PCV20. At the VAX-31 High Dose, average OPA immune responses were greater for 18 of 20 serotypes compared to PCV20 (GMR greater than 1.0), with seven of these serotypes achieving statistically higher immune responses compared to PCV20 (lower bound of the 2-sided 95% confidence interval of the OPA GMR is greater than 1.0). At the Middle Dose, 13 of 20 serotypes had a GMR greater than 1.0 and five serotypes achieved statistically higher immune responses compared to PCV20. At the Low Dose, 18 of 20 serotypes met the OPA response non-inferiority criteria, 8 of 20 serotypes had a GMR greater than 1.0 and three serotypes achieved statistically higher immune responses.

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Figure 16.

As shown in Figure 17, for all 11 incremental serotypes unique to VAX-31, and not in PCV20, all three doses met the superiority criteria (lower bound of the 2-sided 95% confidence interval of the difference in the proportions of participants with a ≥4-fold increase from day 1 to month 1 is greater than 10%, and lower bound of the 2-sided 95% confidence interval of the OPA GMR is greater than 2.0).

Figure 17.

Based on these positive results, we selected the High Dose of VAX-31 to advance to an adult Phase 3 program. Following an FDA End-of-Phase 2 meeting, we are advancing a comprehensive Phase 3 adult clinical program for VAX-31 to support a planned BLA submission. The announced Phase 3 clinical studies, which were finalized in consultation and alignment with the FDA, include the pivotal, noninferiority trial evaluating VAX-31 for the prevention of IPD and pneumonia in adults (OPUS-1); a trial evaluating VAX-31 when administered concomitantly with a licensed, high-dose seasonal influenza vaccine in pneumococcal-naïve adults (OPUS-2); and a trial in adults who have previously received a pneumococcal vaccine (OPUS-3), all of which are currently enrolling participants. Across these three studies, approximately 6,000 adults are expected to be enrolled in total, of whom approximately 3,400 will receive VAX-31, with the intent to generate a broad and robust safety, tolerability and immunogenicity dataset. We are also planning for a manufacturing consistency study (e.g., a lot-to-lot study).

OPUS-1 is evaluating the safety, tolerability and immune responses of VAX-31 in approximately 3,560 adults aged 50 and older through direct, head-to-head comparisons with both PCV21 and PCV20, the current standard-of-care PCVs, with the objective of establishing a best-in-class profile for VAX-31. The trial is also evaluating the safety, tolerability and immune responses of VAX-31 in approximately 440 adults aged 18-49. OPUS-1 is being conducted at approximately 50 sites in the United States.

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The key primary immunogenicity objectives of this trial are to demonstrate (i) noninferiority if the lower bound of the two-sided 95% confidence interval for the OPA GMR of VAX-31 exceeds 0.667 compared with PCV21 and/or PCV20 for the 28 serotypes shared with one or both comparators and (ii) superiority if the lower bound of the two-sided 95% confidence interval of the OPA GMR exceeds 2.0 for the three serotypes unique to VAX-31 and serotype 20B versus the comparator vaccines. The trial is also evaluating the safety, tolerability and immune responses of VAX-31 in adults aged 18-49. Key secondary immunogenicity objectives are included to evaluate VAX-31 based on additional measures of non-inferiority, superiority and statistically greater immune responses.

OPUS-2 is a randomized, double-blind, placebo-controlled clinical trial designed to evaluate the safety, tolerability and immunogenicity of VAX-31 when administered either concomitantly with or one month following administration of a licensed, high-dose seasonal influenza vaccine in pneumococcal-naïve, healthy U.S. adults aged 50 years and older. The study is expected to enroll approximately 1,300 participants at approximately 25 sites in the United States. The results of this descriptive study are intended to inform the design of a potential post-licensure outcomes study that further evaluates VAX-31 in concomitant use with an influenza vaccine and to provide supportive evidence as part of the broader Phase 3 dataset.

OPUS-3 is a randomized, double-blind, active-controlled, descriptive clinical trial designed to evaluate the safety, tolerability and immunogenicity of a single dose of VAX-31 in approximately 720 healthy U.S. adults aged 50 years and

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older with a history of prior pneumococcal vaccination at least six months prior. The study will be conducted at approximately 30 sites in the United States.

Contextual Information: VAX-24 Adult Indication

Phase 1/2 Clinical Proof-of-Concept Study in Adults Aged 18 to 64

Our first-in-human study was a randomized, double-blind, dose-finding, controlled Phase 1/2 clinical proof-of-concept study designed to evaluate the safety, tolerability and immunogenicity of VAX-24 in healthy adults aged 18 to 64. The Phase 1 portion of the study evaluated the safety and tolerability of a single injection of VAX-24 at three dose levels, 1.1mcg, 2.2mcg and 2.2mcg/4.4mcg, and compared to PCV20 in 64 healthy adults aged 18 to 49. Participants were randomized equally in four separate arms and were evaluated for safety 8 and 29 days after dosing. The Phase 2 portion evaluated the safety, tolerability and immunogenicity of a single injection of VAX-24 at the same three dose levels and compared to a single injection of PCV20 in 771 healthy adults 50 to 64 years of age. Participants were randomized equally in four separate arms and approximately 28 days after participants were dosed, samples were collected to assess immunogenicity. The immunogenicity objectives of the Phase 2 portion of the study included an assessment of the induction of antibody responses, using OPA and IgG, at each of the three VAX-24 doses and compared to PCV20, and for the additional four serotypes contained in VAX-24 (and PPSV23), but not in PCV20, the percentage of subjects that experienced a four-fold rise in antibody titers. Participants in the study were evaluated for safety through six months after vaccination.

Figure 18 is a schematic of the overall study design of our Phase 1/2 study:

In October 2022, we announced positive topline results from both the Phase 1 and Phase 2 portions of the study.

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VAX-24 met the primary safety and tolerability objectives, demonstrating a safety profile similar to PCV20 for all doses studied. Frequently reported local and systemic reactions were generally mild-to-moderate, resolving within several days of vaccination, with no difference observed across the cohorts. No serious adverse events or new onset chronic illnesses were considered to be related to study vaccines.

Figure 19.

In this study, VAX-24 demonstrated robust OPA and IgG immune responses for all 24 serotypes at all doses studied (1.1mcg, 2.2mcg, 2.2mcg/4.4mcg). At the conventional 2.2mcg dose, which we plan to advance to a potential Phase 3 program, VAX-24 met or exceeded the established regulatory immunogenicity standards for all 24 serotypes. At this dose, VAX-24 met the standard OPA response non-inferiority criteria for all 20 serotypes common with PCV20, of which 16 serotypes (3, 4, 6B, 7F, 8, 9V, 10A, 11A, 12F, 14, 15B, 18C, 19A, 19F, 23F and 33F) achieved higher immune responses and four serotypes (9V, 18C, 19F and 33F) reached statistical significance. Additionally, at all three doses, VAX-24 met the standard superiority criteria for all four serotypes (2, 9N, 17F and 20B) unique to VAX-24.

Figure 20.

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Figure 21.

Regulatory Threshold for Superiority (LL95%CI > 10%)

Based on the results of this study, the FDA granted a BTD for VAX-24 for the prevention of IPD in adults.

Phase 2 Clinical Study in Adults 65 and Older

To add to the body of data in adults, we conducted a separate Phase 2 study in adults aged 65 and older. This study was a randomized, double-blind, dose-finding, controlled Phase 2 study designed to evaluate the safety, tolerability and immunogenicity of a single injection of VAX-24 at the same three dose levels evaluated in the Phase 1/2 study, 1.1mcg, 2.2mcg and 2.2mcg/4.4mcg, and compared to a single injection of PCV20 in 207 healthy adults aged 65 and older. Participants were randomized equally in four separate arms and approximately 28 days after participants were dosed, samples were collected to assess immunogenicity. The immunogenicity objectives of the study include an assessment of the induction of antibody responses, using OPA and IgG, at each of the three VAX-24 doses and compared to PCV20, and for the additional four serotypes contained in VAX-24 (and PPSV23), but not in PCV20, the percentage of subjects that experience a four-fold rise in antibody titers. This study was designed to inform the powering of a Phase 3 study and was not powered to demonstrate non-inferiority. Participants in the study also were evaluated for safety through six months after vaccination.

Figure 22 is a schematic of the overall study design of our Phase 2 study in adults aged 65 and older:

Figure 22.

On April 17, 2023, we announced positive results from this Phase 2 study of VAX-24 in adults aged 65 and older, as well as data from the full six-month safety assessment and prespecified pooled immunogenicity analyses from both the Phase 2 study in adults aged 65 and older and the prior Phase 1/2 study in adults aged 18-64.

In this Phase 2 study, VAX-24 demonstrated robust OPA immune responses across all 24 serotypes at all doses studied (1.1mcg, 2.2mcg, and 2.2mcg/4.4mcg), confirming the prior Phase 2 adult study results. The VAX-24 2.2mcg dose, which we had planned to advance to a potential Phase 3 program prior to our decision to advance exclusively VAX-31, showed an overall improvement in immune responses compared to PCV20 relative to the results from the prior Phase 2 study in adults

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aged 50-64. The six-month safety data from both adult studies showed safety and tolerability results for VAX-24 similar to PCV20 at all doses studied.

Figure 23.

Consistent with prior Phase 2 study, the 2.2mcg dose demonstrated higher OPA GMR for 16 out of the 20 shared serotypes. The 2.2mcg dose showed robust immune responses for all 24 serotypes.

Figure 24.

Figure 25.

Threshold for Superiority (LL95%CI > 10%)

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Prespecified Pooled Immunogenicity Analyses of Data from VAX-24 Adult Phase 2 Studies

Additionally, we conducted prespecified pooled analyses of data from both adult Phase 2 studies to evaluate the immunogenicity of VAX-24 in participants aged 50 and older and aged 60 and older, which are representative populations for the potential VAX-24 Phase 3 pivotal study. The prespecified pooled immunogenicity analyses of data from both adult Phase 2 studies showed the VAX-24 2.2mcg dose met the OPA non-inferiority criteria for all 20 serotypes common with PCV20 and met the superiority criteria for the four additional serotypes unique to VAX-24. In the pooled group with participants aged 50 and older, VAX-24 met the OPA response non-inferiority criteria for all 20 serotypes common with PCV20, of which 16 achieved higher immune responses and four reached statistical significance. In the pooled group with participants aged 60 and older, VAX-24 met the OPA response non-inferiority criteria for all 20 serotypes common with PCV20, of which 17 achieved higher immune responses and three reached statistical significance.

Figure 26.

Combined Six-Month Safety Data from Both Adult VAX-24 Studies

In April 2023, we also reported the full six-month safety results from the VAX-24 Phase 2 study in adults aged 65 and older and the VAX-24 Phase 1/2 study in adults aged 18-64. Through six months, VAX-24 demonstrated safety and tolerability results similar to PCV20 across all ages and doses studied. Frequently reported local and systemic reactions were generally mild-to-moderate, resolving within several days of vaccination, with no meaningful difference observed across the cohorts. Further, no serious adverse events or new onset chronic illnesses were considered to be related to study vaccines. In a VAX-24 arm of the Phase 2 study in adults aged 65 and older, one participant with multiple pre-existing risk factors suffered a sudden cardiac death six months post-vaccination, which the Principal Investigator determined was not related to study vaccine due to the participant’s history of hypertensive cardiovascular disease.

Figure 27.

Related MAAE, n (%) 0 0 1 (0.4) 0

Related NOCI, n (%) 0 0 0 0

Related SAE, n (%) 0 0 0 0

Related Death, n (%) 0 0 0 0

(1) 66-year-old white, obese male (BMl: 47.4) with hypertension. No solicited AEs were reported after vaccination. Participant suffered sudden cardiac death six months post-vaccination determined by Principal Investigator to be not related to study product due to participant's history of hypertensive cardiovascular disease.

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TEAE = Treatment emergent adverse events

Excludes Solicited AEs

Clinical Programs: Infant Indication

We expect the clinical development of VAX-24 and VAX-31 in infants to follow similar approaches utilized for PCV13, PCV15 and PCV20, where vaccine effectiveness against IPD was inferred from immunologic correlates, and approvals are based on non-inferiority comparisons of IgG responses and totality of data, whereas in the adult population approvals have been based on non-inferiority comparisons of OPA responses. Consistent with the approval processes for PCV13, PCV15 and PCV20 in infants, we do not anticipate that clinical field efficacy trials will be required for VAX-24 or VAX-31 in the pediatric population.

Our Phase 3 and commercial strategy for VAX-24 or VAX-31 for the infant indication will depend on several factors, including the results from our ongoing Phase 2 study for VAX-31. Pending the outcome of our Phase 2 VAX-31 study, we plan to initiate a Phase 3 program with an Optimized Dose formulation of VAX-24 or VAX-31. We expect our Phase 3 program in the pediatric population to focus on evaluating non-inferiority to PCV20, the current standard of care in infants, for immunogenicity and seroconversion or antibody concentration threshold; assessing U.S. routine vaccination responses following concomitant administration with our vaccine candidate; and generating a sufficient safety database in infants. The Phase 3 non-inferiority results would then be used to seek approval in the pediatric population. This approach is similar to the approach utilized to develop PCV13, where the immunogenicity of PCV13 was compared to the original 7-valent Prevnar product, which was the standard of care at the time, as well as the approaches for PCV15 and PCV20, which were compared to PCV13.

VAX-24

The VAX-24 Phase 2 infant study was a randomized, observer-blind, dose-finding two-stage clinical study evaluating the safety, tolerability and immunogenicity of VAX-24 at three dose levels, 1.1mcg, 2.2mcg, and 2.2mcg/ 4.4mcg, and compared to PCV15 and PCV20 in healthy infants. The Stage 1 portion of the study evaluated the safety and tolerability of a single injection of VAX-24 at three dose levels compared to PCV15 in 48 infants in a dose-escalation approach. The Stage 2 portion evaluated the safety, tolerability and immunogenicity of VAX-24 at three dose levels and compared to PCV20 in 789 healthy infants. In line with recommendations from the ACIP, the study design included a primary immunization series consisting of three doses given at two months, four months and six months of age, followed by a subsequent booster dose at 12-15 months of age. The key prespecified immunogenicity study endpoints included an assessment of immune responses for all three VAX-24 doses and compared to PCV20 on the shared serotypes measured at 30 days post-dose three (“PD3”) and post-dose four (“PD4”). Immune responses were assessed based on anti-pneumococcal polysaccharide serotype-specific IgG responses (proportion of participants achieving the accepted IgG threshold value of ≥0.35mcg/ml) at 30 days PD3 and IgG geometric mean titer ratios at 30 days PD4. All participants in the study were evaluated for safety through six months following the booster dose.

Figure 28 is a schematic of the overall study design of our VAX-24 infant Phase 2 study:

Figure 28.

In March 2025, we announced positive topline, interim data from the VAX-24 infant Phase 2 study and, in November 2025, we announced final safety, tolerability, and immunogenicity results that were consistent with the positive interim

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data reported in March 2025 and showed that VAX -24 elicited robust, dose-dependent immune responses, with little to no evidence of carrier suppression observed. The final data analysis included full 6-month safety results and complete post-dose 3 (primary immunization series) and post-dose 4 (booster dose) IgG and OPA results. The key immunogenicity endpoints included an assessment of immune responses for each of the VAX-24 dose levels (Low, Mid, Mixed) in comparison with PCV20 for the 20 common and 4 unique serotypes in VAX-24. At 1-month post-dose 3 and post-dose 4, immune responses were assessed based on serotype-specific IgG seroconversion rates (IgG threshold value of ≥0.35mcg/mL). IgG GMRs were also assessed at 1-month post-dose 3 and post-dose 4, along with other key immunogenicity endpoints, including OPA.

Post-dose 3, all VAX-24 doses met target precedent Phase 2 non-inferiority (NI) criteria on relative seroconversion rates (lower limit of the 95% confidence interval for the difference between the proportion of participants achieving the pre-defined seroconversion rate (IgG concentration ≥0.35 mcg/mL) for the highest circulating serotypes, as defined by the percentage of IPD caused in individuals <5 yrs of age in the U.S. in 2023 based on ABC surveillance data, contained in VAX-24. The Low and Mid doses met the seroconversion rate criteria for 20 of 24 serotypes overall and the Mixed Dose met such criteria for 19 of 24 serotypes. The Mid and Mixed Doses met the target Phase 2 IgG GMR point estimate of >0.6 for 21 of 24 serotypes.

Post-dose 4, all VAX-24 doses met our target Phase 2 IgG GMR point estimate of >0.6 for the three highest circulating serotypes contained in VAX-24. The Mixed Dose met this target for 19 of 24 serotypes overall and the Mid dose met this target for 18 of 24 serotypes. Post-dose 4, VAX-24 elicited robust memory responses across all doses for all serotypes.

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Additionally, the four incremental serotypes unique to VAX-24 that provide expanded serotype coverage relative to PCV20 elicited robust immune responses and met all target criteria across all endpoints at all doses evaluated.

In this study, VAX-24 was well-tolerated and demonstrated a safety profile similar to PCV20 across all doses studied. Frequently reported local and systemic reactions were generally mild-to-moderate, resolving within several days of vaccination, with no meaningful differences observed across the cohorts. No serious adverse events were considered to be related to study vaccines.

The final positive data from the VAX-24 infant Phase 2 dose-finding study further validated our rationale for exploring higher doses in the ongoing VAX-31 infant Phase 2 study.

VAX-31

The VAX-31 Phase 2 infant study is a randomized, double-blind, active controlled, dose-finding, three-stage clinical study evaluating the safety, tolerability and immunogenicity of VAX-31 compared to PCV20 in healthy infants. Stage 1 of the study evaluated the safety and tolerability of VAX-31 at three dose levels (Low, Middle and High) and compared to PCV20 in 48 infants in a dose-escalation approach. In the Low, Middle and High Doses, all serotypes were dosed at 1.1mcg, 2.2mcg and 3.3mcg, respectively, except serotypes 1, 5 and 22F, which were dosed at 1.65mcg, 3.3mcg, and

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4.4mcg, respectively. Participants who received VAX-31 in Stage 1 continued the standard dosing regimen as part of Stage 2. Stage 2 is evaluating the safety, tolerability and immunogenicity of VAX-31 at the same three dose levels and compared to PCV20. In line with recommendations from the ACIP, the study includes a primary immunization series consisting of three doses given at two, four and six months of age, followed by a subsequent booster dose at 12-15 months of age. On September 2025, we announced advancement of the VAX-31 infant Phase 2 randomized, dose-finding study to the third and final stage following modifications to the protocol to add a new dose arm to evaluate the VAX-31 Optimized Dose (majority of serotypes dosed at 4.4mcg and the balance dosed at 3.3mcg) and discontinue enrollment in the Low Dose arm. The Middle and High Dose arms are continuing as planned.The key prespecified immunogenicity study endpoints include an assessment of immune responses for each of the VAX-31 dose levels in comparison with PCV20 for the 20 common and 11 unique serotypes in VAX-31. Post-primary series PD3 immune responses will be assessed based on serotype-specific IgG seroconversion rates (proportion of participants achieving the accepted IgG threshold value of ≥0.35mcg/mL) at 30 days PD3. IgG geometric mean titers will be assessed at 30 days PD3 and PD4, along with other key immunogenicity endpoints. All participants in the study will be evaluated for safety through six months following the booster dose.

Figure 29 is a schematic of the overall study design of our VAX-31 infant Phase 2 study:

Figure 29

We expect to announce topline safety, tolerability and immunogenicity data for the Phase 2 randomized, dose-finding study from the primary three-dose immunization series and booster dose either sequentially or together by the end of the first half of 2027.

Pending the VAX-31 infant study readout, we plan to initiate a Phase 3 program with an Optimized Dose formulation of VAX-24 or VAX-31.

Platform Application Two: Novel Conjugate Vaccine Opportunities

We are also developing novel conjugate vaccine candidates for other diseases for which there are no existing vaccines. By leveraging our platform, we have been able to generate novel protein carriers with site-specific incorporation of nnAAs designed to provide optimal exposure of both B-cell and T-cell epitopes on the carrier. Using these novel protein carriers, we can produce highly stable conjugate vaccine candidates through site-specific conjugation of antigens, including polysaccharides. Functionally, one significant advantage of using carriers may be the additional protective immunity that the protein itself can provide beyond the conjugated antigen itself.

Group A Strep Disease Background and Market Opportunity

Streptococcus pyogenes (S. pyogenes or Group A Strep) bacteria cause a wide spectrum of both acute and chronic clinical conditions that lead to considerable disease burden globally. Group A Strep causes an estimated 800 million cases of illness each year and is one of the leading infectious disease-related causes of death and disability worldwide. It is estimated that over 600,000 deaths globally result from Group A Strep, and, even in countries where antibiotic treatment is readily available, Group A Strep has a considerable disease burden contributing more than 600 million cases of pharyngitis per year along with substantial morbidity from cellulitis, invasive disease, and skin infections. The total annual market for a Group A Strep vaccine is estimated at approximately $3 billion to $4 billion globally. The annual economic burden of Group A Strep disease in the U.S. population is estimated to exceed $6 billion resulting from invasive disease and non-severe acute upper respiratory infections. In addition, Group A Strep drives significant antibiotic use, especially among children, and as such contributes towards increased antimicrobial resistance. Among older adults (≥ 65 years) in the United

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States, rates of invasive disease and deaths caused by Group A Strep have been increasing over the last decade. Some of the most serious consequences of Group A Strep include invasive diseases such as flesh-eating disease (necrotizing fasciitis), sepsis and sequelae such as rheumatic heart disease ("RHD"). An estimated 55 million people are affected by RHD each year worldwide. Importantly, the majority of Group A Strep infections lead to pharyngitis, commonly known as strep throat, which is highly prevalent in school-age children. In the United States, an estimated 17% of outpatient antibiotic prescriptions dispensed to children aged 3 to 9 years are for the treatment of suspected Group A Strep infections. Studies have indicated that antibiotic resistance to Group A Strep has significantly increased over the past decade, leading the CDC to categorize Group A Strep as a concerning threat. Additionally, the development of vaccines against Group A Strep has become a priority for the WHO amid recognition of the rising disease incidence globally, as well as the need to combat avoidable antibiotic consumption.

It has been established that the repeated natural infection of children with Group A Strep results in immune responses that are protective against subsequent Group A Strep infection. We believe this observation justifies the development of a rationally designed vaccine for Group A Strep that is focused on conserved antigens expressed by all strains of the bacteria.

VAX-A1

We have developed a conjugate vaccine candidate, VAX-A1, designed to confer broad protection against subtypes of Group A Strep by virtue of polyrhamnose, a conserved polysaccharide, conjugated to Group A Strep specific immunogenic protein carrier using our site-specific conjugation technology. The resulting conjugate is designed to ensure optimal exposure of both the B-cell and T-cell epitopes on the protein carrier to confer robust, boostable and durable protective immune responses. We believe this single conjugate could potentially cover all Group A Strep strains. The vaccine is a combination of this novel protein-polysaccharide conjugate along with two additional conserved surface proteins.

Our initial preclinical proof-of-concept study was published in the journal Infectious Microbes & Diseases in December 2020. In the study, a novel protein and polysaccharide conjugate of the Group A Strep polysaccharide was constructed for inclusion in a universal subunit vaccine against infections by the pathogen. The VAX-A1 vaccine candidate, based on SpyAD-conjugated to a modified polyrhamnose backbone (lacking N-acetyl glucosamine) and including SLO and C5a peptidase, demonstrated protection from subcutaneous and systemic challenge in mice, antibody binding and opsonophagocytic killing for multiple Group A Strep M Protein Gene types and no evidence of cross-reactivity to human heart and brain tissue antigens (Figure 30), which is a key leading indicator of vaccine safety. The study was carried out in collaboration with researchers at the Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California School of Medicine and the Skaggs School of Pharmacy and Pharmaceutical Sciences at the University of California, San Diego.

Figure 30.

Our VAX-A1 vaccine development program has been funded in part by a grant obtained from Combating Antibiotic Resistant Bacteria Biopharmaceutical Accelerator (“CARB-X”), a global non-profit partnership dedicated to accelerating antibacterial innovation to tackle the rising global threat of drug-resistant bacteria.

We nominated the final vaccine candidate for our VAX-A1 program and initiated IND-enabling activities in 2021 and plan to initiate a Phase 1 adult clinical study in 2026, with the primary objective of assessing safety and tolerability.

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Platform Application Three: Protein Vaccine Opportunities

We believe we can also develop novel protein vaccine candidates constructed using “tough-to-make” protein antigens uniquely able to be expressed using the platform. In particular, the lack of a cellular membrane in our platform allows for the exogenous addition of components to manipulate transcription, translation and folding by modification of reaction conditions. Furthermore, removal of the typical restriction to maintain cell viability also creates unique avenues for optimizing and promoting protein production for antigens that might be cytotoxic to a cell-based system or require non-physiological conditions for optimal protein folding. Thus, utilizing these advantages, we believe we can express and purify important protein targets to generate unique candidates that are beyond the scope of traditional production systems.

VAX-GI

VAX-GI is a novel preclinical vaccine candidate being developed as a preventative treatment for dysentery and shigellosis, which is caused by Shigella bacteria. Shigella is a bacterial illness that causes dysentery with symptoms, including bloody diarrhea, fever, and stomach cramps. Currently there are no prophylactics and treatment is primarily oral rehydration therapy, with antibiotics (mainly ciprofloxacin and azithromycin) used to shorten the duration of infection. However, the growing incidence of antibiotic resistance has complicated this approach with an increasing rate of extensively drug resistant. Shigella is estimated to cause 80 million to 165 million cases of disease and 600,000 deaths annually, mostly among children. Further, in young children Shigella can cause malnutrition and induce or exacerbate stunting, leading to a long-term impact on both physical and cognitive development. This has resulted in the WHO including Shigella vaccine development as a priority goal.

VAX-GI, which includes cell-free produced IpaB conjugated to Shigella flexneri 2a polysaccharide was used to vaccinate mice which were evaluated for generation of a productive immune response and protection. All groups were challenged i.n. (pulmonary infection model) with virulent S. flexneri 2a 2457T or S. sonnei Moseley on day 57 postvaccination. Immunization with S. flexneri 2a OPS-IpaB conjugate vaccine afforded 78% protection against homologous S. flexneri 2a challenge (P < 0.0001) whereas S. flexneri 2a OPS-CRM provided only 50% protection (P = 0.0014) (Figure 33A). IpaB alone conferred 67% protection against S. flexneri 2a (P = 0.0003) (Figure 33A). The trend of higher protective efficacy of OPS-IpaB than of OPS-CRM or IpaB alone suggests that both OPS and IpaB contribute to the observed protective immunity. IpaB- and OPS-specific IgG titers in mice that were protected were significantly higher than titers in those that succumbed to infection (Figure 33C). Importantly, S. flexneri 2a OPS-IpaB exhibited 56% protection against heterologous S. sonnei challenge (P < 0.0001) (Figure 33B). Because Shigella O-polysaccharide immunity is serotype specific, this cross protection is attributable to IpaB. This is consistent with the lack of protection in the OPS-CRM group (11% survival). IpaB alone afforded 44% protection against S. sonnei (P = 0.0003) (Figure 33B), which was not significantly different from the protection elicited by S. flexneri 2a OPS-IpaB. IpaB-specific serum IgG was again significantly higher in mice that were protected against S. sonnei infection (Figure 33D). S. flexneri 2a and S. sonnei IpaBs share >98% homology; therefore, cross protection was expected. The slight difference in IpaB efficacy in the two experiments is likely due to the higher severity of S. sonnei infection (mice succumbed sooner). Unvaccinated control mice had very low to no survival. We plan to pursue conjugate and protein-only approaches simultaneously, as shown in Figure 34.

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Figure 33.

Figure 34.

VAX-GI is being developed in collaboration with the University of Maryland, Baltimore as well as with partial funding from two research grants awarded by the NIH. As part of our continued focus on strategic capital deployment and in order to prioritize our resources towards our PCV franchise, we announced in August 2025 that we had paused the advancement, beyond preclinical development, of VAX-GI while remaining confident in its potential and preserving the option to advance the program in the future.

Manufacturing and Supply

We have designed and developed a proprietary, scalable and portable manufacturing process for VAX-31 and VAX-24 that we believe can scale to address clinical and commercial vaccine supply needed to serve both adult and pediatric populations.

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VAX-31 and VAX-24 Process

The manufacturing process for our VAX-31 and VAX-24 vaccine candidates consists of four key components: (i) our proprietary eCRM protein carrier; (ii) the 31 or 24 pneumococcal polysaccharides; (iii) the 31 or 24 conjugate drug substances; and (iv) the mixture of these 31 or 24 drug substances into the final drug product.

eCRM

Our proprietary eCRM protein carrier is produced using our cell-free protein synthesis platform, which is exclusively licensed from Sutro Biopharma for the Vaccine Field (as defined in the Sutro Biopharma License Agreement (as defined below)). eCRM, contains multiple copies of non-native para azido-methyl-phenylalanine (“pAMF”) amino acid. The pAMF amino acids have a specific structure that enables eCRM to participate in the site-specific click chemistry conjugation reaction with activated pneumococcal polysaccharides.

The cell-free reaction is performed in a manner analogous to traditional fermentation but without the cells. The first step in the production of eCRM is the manufacture of critical raw materials, namely E. coli extracts and lysates that contain the cellular machinery required for in vitro DNA transcription and translation. The eCRM protein is then manufactured by combining these E. coli extracts and lysates with classic media components such as amino acids, minerals and salts, with the in vitro reaction driven by the addition of plasmid DNA coding for the eCRM protein’s amino acid sequence. This cell-free reaction takes place in a standard fermenter, followed by standard protein purification chromatographic and filtration processes. The manufacturing process has consistently yielded a product of the desired quality.

Pneumococcal Polysaccharides

Each of the 31 or 24 pneumococcal polysaccharides is individually isolated from Streptococcus pneumoniae bacterial strains. Each individual Streptococcus pneumoniae strain is cultured in a bioreactor using an improved single standardized fed-batch bioreactor process and a single standardized downstream purification process. Overall, this standardized upstream and downstream process is simple and streamlined, thereby reducing manufacturing cost of goods and providing an efficient path of progression for the program from process characterization and validation through to commercialization, if our vaccine candidates are approved.

Conjugate Drug Substances

Each of the 31 or 24 conjugate drug substances is manufactured individually, as monovalent conjugates, by conjugating each of the 31 or 24 activated pneumococcal polysaccharide strains, one at a time, to the eCRM carrier protein.

Click chemistry provides for a conjugation reaction that is quick, consistent and high-yielding, and which we optimized to be largely standardized across the various polysaccharides. Through statistical design of experiment studies, we have gained a significant understanding of which variables to adjust to maximize product quality and, accordingly, immunogenicity in rabbit models.

Drug Product

All 31 or 24 conjugate drug substances are mixed, formulated with appropriate excipients and adsorbed onto alum. Clinical doses are filled in vials and stored refrigerated.

Key Agreements

We currently do not own or operate any manufacturing facilities, but our strategic partnerships with Lonza and other contract manufacturing organizations (“CMOs”) provide us with access to substantial resources to facilitate an independent supply path to the market. We have entered into agreements with Lonza, a leading global contract manufacturer with deep domain expertise and experience in large and small-scale production of clinical, as well as commercial-stage products, to secure capacity, technical expertise and resources to support the production of eCRM, polysaccharides and drug substance for our PCV programs. We have also entered into a commercial manufacturing agreement with Lonza to support the potential global commercialization of our PCV candidates in both the adult and pediatric populations. This agreement complements our plans to utilize existing Lonza infrastructure to advance clinical development and the anticipated initial U.S. launch of VAX-31 for the adult population. We have relationships with other leading CMOs for the production of the final drug product for our PCV candidates, for the extract and lysates that we use to manufacture eCRM and for certain raw materials. We have an agreement with Sutro Biopharma pursuant to which Sutro Biopharma supplies us with extract and custom reagents for use in manufacturing preclinical and certain clinical supply of vaccine compositions. In December

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2019, we exercised our right to require Sutro Biopharma to establish a second supplier for extract and custom reagents to support future clinical and commercial needs and thereafter initiated a tech transfer to a CMO as a second supplier of extract. In December 2022, we entered into a separate agreement with Sutro Biopharma pursuant to which we enhanced our rights with the second supplier of extract and acquired an option to access expanded rights to develop and manufacture extract, among other rights. In November 2023, we exercised this option and entered in a manufacturing rights agreement to obtain control over manufacturing and development of cell-free extract for our vaccine candidates. In September 2025, we announced a new agreement with Patheon Manufacturing Services, LLC, part of Thermo Fisher Scientific (collectively, "Thermo Fisher") to provide custom commercial fill-finish capacity for our broad-spectrum PCVs at Thermo Fisher's Greenville, North Carolina facility.

Lonza Agreements

Development and Manufacturing Services Agreements

In April 2022, we entered into a non-exclusive development and manufacturing services agreement with Lonza effective as of March 22, 2022, which was subsequently amended on May 12, 2022, November 21, 2022 and October 31, 2023 (as amended, the “2022 Lonza DMSA”). Pursuant to the 2022 Lonza DMSA, Lonza is obligated to perform services, including manufacturing process development and clinical manufacture and supply of our proprietary PCV candidates. Subject to the terms and conditions set forth in the 2022 Lonza DMSA, Lonza has granted to us a non-exclusive, worldwide, fully paid-up, irrevocable, transferable license, including the right to grant sublicenses, under the New General Application Intellectual Property, to research, develop, make, have made, use, sell and import the Product. Unless earlier terminated, the 2022 Lonza DMSA shall remain in place for a period of five years. Either party may terminate the 2022 Lonza DMSA for any reason on prior written notice to the other party, provided that Lonza may not exercise such right until a specified future date. In addition, either party may terminate the 2022 Lonza DMSA (i) within a given time period upon any material breach that is left uncured by the other party, or (ii) immediately if the other party becomes insolvent. We may also terminate the 2022 Lonza DMSA upon an extended force majeure event. Upon expiration and/or termination of the 2022 Lonza DMSA and/or any purchase order, we will pay Lonza for all service rendered, all costs incurred, all unreimbursed capital equipment and any cancellation fees (each term as defined in the 2022 Lonza DMSA).

In February 2023, we entered into another non-exclusive development and manufacturing services agreement with Lonza effective as of March 1, 2023 (the “2023 Lonza DMSA”). Pursuant to the 2023 Lonza DMSA, Lonza will perform manufacturing process development and the manufacture of components for our PCV candidates, including the polysaccharide antigens, our proprietary eCRM protein carrier and conjugated drug substances. Subject to the terms and conditions set forth in the 2023 Lonza DMSA, Lonza has granted to us a non-exclusive, worldwide, fully paid-up, transferable license, including the right to grant sublicenses (subject to the prior written consent of Lonza), under the New General Application Intellectual Property, to use, sell and import the Product manufactured under the 2023 Lonza DMSA (but no other products). Unless earlier terminated, the 2023 Lonza DMSA shall remain in place for a period of five years and shall automatically renew for one additional two-year period unless either party provides written notice of non-renewal at least two years prior to the fifth anniversary of the effective date. We may terminate the 2023 Lonza DMSA for any reason on prior written notice to the other party on a Project Plan-by-Project Plan basis. Either party may terminate the 2023 Lonza DMSA (i) within a given time period upon any material breach that is left uncured by the other party, (ii) immediately if the other party becomes insolvent, is dissolved or liquidated, makes a general assignment for the benefit of its creditors, or files or has filed against it, a petition in bankruptcy or has a receiver appointed for a substantial part of its assets, (iii) upon an extended force majeure event, or (iv) if it becomes apparent to either party at any stage in the provision of the Services that it will be impossible to complete the Services for scientific or technical reasons despite exercise of best commercial efforts by both parties. Pursuant to the reason for termination and the party initiating the termination, we will pay Lonza for some combination of services rendered, costs incurred, unreimbursed capital equipment and/or any cancellation fees. Upon an extended force majeure event, neither party shall have any further liability to the other party (each term as defined in the 2023 Lonza DMSA).

Under each of the 2022 Lonza DMSA and 2023 Lonza DMSA (collectively, the “Lonza Agreements”), we pay Lonza agreed-upon fees for their performance of development and manufacturing services and pass-through expenses incurred by Lonza for raw materials, as well as customary procurement and handling fees. Under each Lonza Agreement, we own all rights, title and interest in and to any and all New Customer Intellectual Property (as defined in each Lonza Agreement), and Lonza owns all rights, title and interest in New General Application Intellectual Property (as defined in each Lonza Agreement).

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Commercial Manufacturing and Supply Agreement

On October 13, 2023, we entered into a pre-commercial services and commercial manufacturing supply agreement with Lonza (the “Lonza Commercial Manufacturing and Supply Agreement”).

Pursuant to the Commercial Manufacturing and Supply Agreement, Lonza will (i) construct and build out a dedicated suite (the “Suite”) at Lonza’s facilities in Visp, Switzerland to manufacture certain key components (including drug substance) for our proprietary PCV franchise and any other products or intermediates we may choose (collectively, the “Products”) and (ii) maintain and operate the Suite (utilizing Lonza’s employees) to manufacture the Products as a service provided to us, including conducting related quality control and quality assurance operations. Lonza will be a preferred, non-exclusive, supplier of the Products to us, and we retain the right to procure the Products from one or more alternate and/or backup manufacturers of the Products (including at our own facilities).

Under the Lonza Commercial Manufacturing and Supply Agreement, prior to completion of construction and certification of the Suite for commercial operation, we will contribute to the capital expenditure costs to construct the Suite (and will own certain equipment in the Suite to be purchased or otherwise acquired by us), and will pay Lonza a fixed-rate monthly service fee for Lonza’s pre-commercial services prior to commencement of commercial operations (which monthly service fee amount is subject to increases in subsequent years). Following commencement of commercial operations of the Suite to manufacture the Products, we will pay Lonza (i) Suite fees based on allocations of certain of Lonza’s costs to maintain the facility in which the Suite is located and to provide shared services to us and Lonza’s other customers in such facility, (ii) service fees based upon Lonza’s actual full-time equivalent employee (“FTE”) costs to operate the Suite to manufacture the Products, and (iii) certain other pass-through costs, including for raw materials. In addition, we may be obligated to pay or reimburse Lonza for certain other fees and expenses under the Lonza Commercial Manufacturing and Supply Agreement. Lonza will be eligible for certain financial bonuses, and subject to certain financial penalties, as incentives for the timely completion of certain scale-up activities, receipt of certain regulatory approvals for the Suite and manufacture of the Products in accordance with our commercial requirements.

Unless earlier terminated, the Lonza Commercial Manufacturing and Supply Agreement will remain in effect until December 31, 2038, subject to automatic renewal for up to three additional renewal periods of five years each, unless we elect not to renew (with 24 months advanced notice to Lonza). We are permitted to terminate the Lonza Commercial Manufacturing and Supply Agreement for convenience or for Lonza’s uncured material breach, in each case subject to certain notice obligations. Lonza is permitted to terminate the Commercial Manufacturing and Supply Agreement in the event that we commit certain specified material breaches, including uncured failure to pay material, undisputed amounts of money due to Lonza, subject to certain notice obligations. Either party may terminate the Commercial Manufacturing and Supply Agreement in certain circumstances in the event of the other party’s bankruptcy. In the event that we terminate the agreement for convenience, or Lonza terminates the agreement in the event that we commit certain specified material breaches, then certain termination consequences may be triggered, including that (i) we would forfeit any outstanding entitlement to credit from Lonza of the Repurposing Fee (as defined below), and (ii) we would be obligated to pay Lonza a termination penalty equal to the greater of (a) CHF 70.0 million, or (b) a prespecified number of months’ FTE fees for the actual FTEs assigned to us as of the date of termination. Within 30 days of the Effective Date, we paid Lonza a repurposing fee (the “Repurposing Fee”) of CHF 27.0 million that will be credited back to us over a 10-year period starting upon commencement of commercial production. In the event of termination under certain circumstances, Lonza shall be obligated to provide certain wind-down and transition services to us for up to 12 and 24 months, respectively.

2026 Development and Manufacturing Services Agreement

On February 18, 2026, we entered into a development and manufacturing services agreement with Lonza, effective as of January 1, 2026, pursuant to which Lonza will perform manufacturing process development and commercial manufacture and supply of certain key components for our proprietary PCV franchise. Under the agreement, we will pay Lonza for development and manufacturing services, in addition to paying for certain raw material and other costs. We will be required to purchase, and Lonza will be required to supply, the components pursuant to the relevant purchase orders under the agreement. In consideration of the commercial supply services and Lonza’s other obligations under the agreement, we will pay Lonza a daily fee for Lonza’s operation of the facility solely to actively manufacture the components. With respect to such commercial supply, and subject to termination rights, we and Lonza have agreed to a mutually binding percentage of annual facility capacity that shall be utilized by Lonza fully and exclusively for Lonza’s performance of services thereunder, which percentages may be adjusted under certain circumstances.

Unless earlier terminated, the agreement will remain in effect until December 31, 2038, subject to automatic renewal for up to three additional renewal periods of five years each, unless we elect not to renew. We may terminate the agreement for convenience, and the agreement contains customary for-cause termination rights for each party. If the Agreement is

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terminated (i) by us for convenience, or (ii) by Lonza for our uncured failure to pay material, undisputed amounts of money due to Lonza, then we shall pay Lonza certain cancellation fees as specified in the agreement.

Sutro Biopharma Agreements

Amended and Restated License Agreement

We are party to an amended and restated license agreement with Sutro Biopharma, dated October 12, 2015, which was subsequently amended on May 9, 2018, May 29, 2018, September 28, 2023 and November 21, 2023 (as amended, the “Sutro Biopharma License Agreement”). Under the Sutro Biopharma License Agreement, we received an exclusive, worldwide, royalty-bearing, sublicensable license under Sutro Biopharma’s patents and know-how relating to cell-free expression of proteins to (i) research, develop, use, sell, offer for sale, export, import and otherwise exploit specified vaccine compositions, such rights being sublicensable, for the treatment or prophylaxis of infectious diseases, excluding cancer vaccines, and (ii) manufacture, or have manufactured by an approved contract manufacturing organization, such vaccine compositions from extracts supplied by Sutro Biopharma pursuant to the Sutro Biopharma Supply Agreement (as described below). We are obligated to use commercially reasonable efforts to develop, obtain regulatory approval for and commercialize the vaccine compositions. In consideration of the rights granted under the Sutro Biopharma License Agreement, we are obligated to pay Sutro Biopharma a 4% royalty on worldwide aggregate annual net sales of our vaccine products for human health and a 2% royalty on such net sales of vaccine products for animal health. Such royalty rates are subject to specified reductions, including standard reductions for third-party payments and for expiration of relevant patent claims. We are also obligated to pay Sutro Biopharma any royalties due to Stanford University (the upstream licensor of Sutro Biopharma), to the extent the royalties payable by Sutro Biopharma to Stanford University are greater than the royalties payable by us to Sutro Biopharma. Royalties are payable on a vaccine composition-by-vaccine composition and country-by-country basis until the later of expiration of the last valid claim in the licensed patents covering such vaccine composition in such country and 10 years after the first commercial sale of such vaccine composition. The latest expiration date of a licensed Sutro Biopharma patent application, if issued, would be 2036, subject to any adjustment or extension of patent term that may be available in a particular country. In addition, we are obligated to pay Sutro Biopharma a percentage of net sublicensing revenue received in the low teen percentages. In addition, in the event we sublicense our non-manufacturing rights under the Sutro Biopharma License Agreement before a specified date, we are obligated to pay Sutro Biopharma a percentage, in the low double-digits, of the sublicensing revenue we receive under such agreement.

On September 28, 2023, we and Sutro Biopharma amended certain terms of the Sutro Biopharma License Agreement, including with respect to (i) royalty reduction provisions applicable in the event of expiration of relevant patent claims, which would result in lower royalties payable by us to Sutro Biopharma under certain circumstances, (ii) the ownership, prosecution, maintenance and enforcement of certain intellectual property rights licensed or arising under the Sutro Biopharma License Agreement (including as agreed to be amended in the Option Agreement (as defined below), and (iii) the timing and form for financial reporting of royalty payment calculations.

The Sutro Biopharma License Agreement will remain in effect until terminated. The agreement may be terminated by either party for the other party’s material breach uncured within 60 days’ notice, by us at will with 60 days’ notice, or by Sutro Biopharma if we challenge Sutro Biopharma’s patents or if we undergo a change of control with a specified competitor of Sutro Biopharma.

Supply Agreement

In May 2018, we entered into a supply agreement with Sutro Biopharma, which was subsequently amended on February 22, 2021 and November 21, 2023 (as amended, the “Sutro Biopharma Supply Agreement”) pursuant to which we purchase from Sutro Biopharma extract and custom reagents for use in manufacturing non-clinical and certain clinical supply of vaccine compositions utilizing the technology licensed under the Sutro Biopharma License at prices not to exceed a specified percentage above Sutro Biopharma’s fully burdened manufacturing cost. If any extracts or custom reagents do not meet the specifications and warranties provided, then we will not have an obligation to pay for the non-conforming product, and Sutro Biopharma will be obligated to replace the non-conforming product within the shortest possible time with conforming product at our cost. The term of the Sutro Biopharma Supply Agreement is from execution until the later of (i) July 31, 2022, or (ii) the date that we and Sutro Biopharma enter into the Phase 3/Commercial Supply Agreement and Sutro Biopharma is supplying to us each Product under the Phase 3/Commercial Supply Agreement (each term as defined in the Sutro Biopharma Supply Agreement). The Sutro Biopharma Supply Agreement may be terminated by either party for the other party’s material breach uncured within 60 days’ notice, by us at will with 60 days’ notice, or by mutual agreement of the parties. In December 2019, we exercised our right to require Sutro Biopharma to establish a second supplier for extract and custom reagents to support our anticipated clinical and commercial needs.

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Option Agreement

In December 2022, we entered into an option grant agreement with Sutro Biopharma (the “Option Agreement”). Pursuant to the Option Agreement, we acquired from Sutro Biopharma (i) authorization to enter into an agreement with an independent alternate CMO to directly source Sutro Biopharma’s cell-free extract, allowing us to have direct oversight over financial and operational aspects of the relationship with the CMO; and (ii) a right, but not an obligation, to obtain certain exclusive rights to internally manufacture and/or source extract from certain CMOs and the right to independently develop and make improvements to extract (including the right to make improvements to the extract manufacturing process as well as cell lines) for use in connection with the exploitation of certain vaccine compositions (the “Option”). We and Sutro Biopharma agreed to negotiate the terms and conditions of a form definitive agreement to be entered into in the event we exercise the Option, which would include the terms and conditions set forth in an executed term sheet between us (the “Term Sheet”) and such terms that were necessary to give effect to each of the terms and conditions set forth in the Term Sheet (the “Form Definitive Agreement”).

As consideration for the Option and other rights and authorizations granted to us under the Option Agreement, we paid Sutro Biopharma upfront consideration of $22.5 million, consisting of (i) $10.0 million in cash and $7.5 million worth of shares of our common stock (the number of shares calculated based on the arithmetic average of the daily volume weighted average price of our common stock as traded on Nasdaq in the three consecutive trading days immediately prior to the issuance thereof) in December 2022, and (ii) $5.0 million in October 2023 within five business days after we and Sutro Biopharma mutually agree in writing upon the Form Definitive Agreement on September 28, 2023. The 167,780 shares of common stock issued was recorded at fair value of $8.0 million on the date of settlement, December 22, 2022.

On November 21, 2023 (the “Option Exercise Date”), we exercised the Option by submitting written notice thereof to Sutro Biopharma and concurrently paid Sutro Biopharma $50.0 million in cash as the first of two installment payments for the Option exercise price, followed by the second and final installment of $25.0 million in cash in May 2024. Upon the occurrence of certain regulatory milestones, certain additional milestone payments may total up to $60.0 million in cash. In the event that we undergo a change of control, certain rights and payments may be accelerated.

Manufacturing Rights Agreement

Concurrent with the payment of the first installment of the Option exercise price pursuant to the Option Agreement, on November 21, 2023, the manufacturing rights agreement (in the form of the Form Definitive Agreement) between us and Sutro Biopharma (the “Manufacturing Rights Agreement”) became effective. Under the Manufacturing Rights Agreement, we received an exclusive (except as to Sutro Biopharma), perpetual (subject to termination), worldwide license, for no additional royalty (i.e., royalty-free, other than any royalties due under the Sutro Biopharma License Agreement), under Sutro Biopharma’s relevant patents and know-how, to manufacture or have manufactured extract and improvements to extract (in any form) solely for use in the research, development, use, production, sale, offering for sale, export, import, commercialization or other exploitation of Vaccine Compositions (as defined in the Sutro Biopharma License Agreement) (as well as certain rights with respect to certain regulatory matters related to extract and its use in connection with such Vaccine Compositions). We have the right to extend our rights and obligations under the Manufacturing Rights Agreement to our affiliates and to sublicense our rights to manufacture extract and improvements to extract to certain third-party CMOs and other contractors (for our benefit and not for such third party’s independent commercial use). For clarity, we are not permitted to manufacture extract for sale to third parties for the independent use of such third parties. Under the Manufacturing Rights Agreement, we have the obligation to protect the confidentiality of the extract manufacturing technology, and Sutro Biopharma has certain audit rights in connection therewith.

Under the Manufacturing Rights Agreement, upon our request and at our cost, Sutro Biopharma will support up to two technology transfers to us (or to an affiliate of ours or certain third-party CMOs designated by us) of certain Sutro Biopharma know-how, materials and information to enable us to manufacture or have manufactured extract. Under certain circumstances, Sutro Biopharma may source extract from us or certain third-party CMOs, subject to reimbursement for technology transfer costs.

The Manufacturing Rights Agreement contains certain terms with respect to the ownership, prosecution, maintenance and enforcement of certain intellectual property rights licensed or arising under the Manufacturing Rights Agreement, which are generally consistent with the Sutro Biopharma License Agreement.

Unless earlier terminated, the Manufacturing Rights Agreement will remain in effect in perpetuity. Sutro Biopharma may only terminate the Manufacturing Rights Agreement in the event of our (i) uncured, intentional, material breach of certain confidentiality provisions resulting in actual, material harm to Sutro Biopharma’s business, (ii) uncured, intentional material breach of certain provisions relating to the use of certain of Sutro Biopharma’s know-how outside of the Vaccine Field, (iii) unintentional, material breach of certain provisions relating to the use of certain of Sutro Biopharma’s know-

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