To Understand the Safety and Effects of a C. Difficile Vaccine With New Adds-Ons That Will Be Given to Healthy Adults
← catalyst calendarNCT05805826 · readout in 1,764 d
Sponsored by Pfizer (industry) · PFE — their whole pipeline →.
Phase
Phase 1/2
Status
Active, not recruiting
Study type
Interventional
Design
Randomized · Triple · Prevention
Enrollment
936actual
Sites
23
Country
United States
Every value on this page is a field the sponsor filed with ClinicalTrials.gov, reproduced. Dates are their own estimates, revised as a study runs, unless the registry marks them actual. sources →
Source: ClinicalTrials.gov, retrieved 2026-08-19
Dates
each axis at the precision it was filed, with the registry's own basis| Date | Filed | Basis | What it is |
|---|---|---|---|
| Start | 2023-03-23 | actual | When the study began enrolling |
| Primary completion | 2031-06-19 | estimated | The date the last participant is measured for the primary outcome — the readout window |
| Study completion | 2031-06-19 | estimated | The whole study's end, after follow-up |
| First posted | 2023-04-10 | actual | When this record first appeared on the registry |
| Results posted | — | When the sponsor posted results to the registry | |
| Record updated | 2026-04-29 | actual | The sponsor's own last edit to this record — every projection above is as current as this date |
What it studies
Condition
- Clostridoides Difficile Associated Disease
Interventions
- Biological: C. difficile vaccine (previously studied formulation).
- Biological: C. difficile vaccine formulation 1.
- Biological: C. difficile vaccine formulation 2.
- Biological: C. difficile vaccine formulation 3.
- Other: Saline Placebo.
Primary outcomes
what the primary-completion date above is the date OFPhase 1: Percentage of participants reporting local reactions
measured For 7 days after each vaccination
Phase 1: Percentage of participants reporting systemic events
measured For 7 days after each vaccination
Phase 1: Percentage of participants reporting adverse events
measured From each vaccination through 1 month after vaccination
Phase 1: Percentage of participants reporting serious adverse events
measured From Dose 1 (Day 1) through 6 months after the last dose
Phase 1: Percentage of participants reporting medically attended adverse events
measured From Dose 1 (Day 1) through 6 months after the last dose of study intervention
Phase 1: Percentage of participants with abnormal hematology and chemistry laboratory values
measured 1 week after Dose 1 (Day 7) and 1 month after each dose (through Month 7)
Phase 2: Percentage of participants reporting local reactions
measured For 7 days after each vaccination
Phase 2: Percentage of participants reporting systemic events
measured For 7 days after each vaccination
Phase 2: Percentage of participants reporting adverse events
measured From each dose of study intervention through 1 month after each dose of study intervention
Phase 2: Percentage of participants reporting adverse events
measured From the first dose of study intervention through 1 month after the last dose of study intervention
Phase 2: Percentage of participants reporting medically attended adverse events
measured From the first dose of study intervention through 6 months after the last dose of study intervention
Phase 2: Percentage of participants reporting serious adverse events
measured From the first dose of study intervention through 6 months after the last dose of study intervention
Phase 2: Geometric mean concentration (GMT) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
measured 1 month after the last dose of study intervention
Phase 2: Geometric mean ratio (GMR) of C. difficile toxin A- and toxin B- specific neutralizing antibodies
measured 1 month after the last dose of study intervention
Phase 2: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
measured From before vaccination to 1 month after the last dose
Phase 2: Geometric mean ratio (GMR) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
measured At Month 7 comparing data from ≥65 years of age to data from 50 through 64 years of age
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