ESTIMATED50% CONFIDENCEClinicalTrials.gov[1] lists 2028-12-11 as the estimated primary completion date; a sponsor's estimate, and trials of this size routinely slip.
- Start
- Dec 11, 202850% CONFIDENCEfrom the source
C.Difficile Vaccine's Phase 3 Trial in Clostridoides Difficile Associated Disease Reads Out
Pfizer's phase 3 trial of C.Difficile Vaccine in clostridoides difficile associated disease reaches primary completion, the point at which the last participant's primary outcome is measured. The trial enrolled 32,500 participants. The purpose of the study is to learn about how effective, safe, and tolerable the Clostridioides difficile (C. difficile) vaccine is in decreasing the number of C. difficile infections (pCDI) in adults 65 years of age or older. The participants will receive either the C. difficile vaccine or placebo (saline). A placebo does not contain any active ingredients. The vaccines will be given as a shot into the upper arm muscle. This study looks at the number of diarrhea (loose stools) events related to a C. difficile infection, so the length of the study can change. If these events happen quickly, the study may finish sooner; if they happen slowly, it could take longer. Sometimes, the study might stop early if the vaccine clearly does not work. Participants will stay in the study until enough events have occurred to answer the main question. On average, each person is expected to take part for
- NCT07282665 is Pfizer's Phase 3, placebo-controlled, double-blinded, randomized study of a Clostridioides difficile vaccine in adults 65 years of age and older, testing efficacy, safety and tolerability in decreasing primary C. difficile infections (pCDI)[1]
- Participants receive either the C. difficile vaccine or a 0.9% sodium chloride saline placebo as an intramuscular injection into the upper arm[1]
- Estimated enrollment is 32,500 participants across 185 sites in the United States, Argentina, Japan and the United Kingdom; the record's status is RECRUITING[1]
- The trial started 2025-12-10 (actual), with primary completion estimated at 2028-12-11 and full completion at 2029-06-07; it was first posted 2025-12-15 and last updated 2026-09-09[1]
- It is event-driven, so "the length of the study can change" - finishing sooner if diarrhea events happen quickly, longer if slowly - and "sometimes, the study might stop early if the vaccine clearly does not work"; each participant is expected to take part for up to about three and a half years[1]
- Primary outcomes are local reactions and systemic events within 7 days of each vaccination, adverse events through 1 month after each vaccination, serious adverse events from Day 1 to 12 months after Vaccination 2 (18 months), and the incidence of the first episode of medically attended and/or clinically meaningful primary CDI from 14 days after Vaccination 2 to the end of surveillance, up to approximately 3.5 years[1]
- Follow-up is 3 planned clinic visits and 3 phone visits, then annual clinic visits; a participant with 3 or more loose stools in 24 hours is asked to save the next one and contact the study site for assessment[1]
References 150% CONFIDENCE
The first entry is always the pin's source. Overall confidence is a weighted average of how firmly each reference supports the start and end times used above; a reference counts half as much for every 180 days older than the newest.
- [1]50%clinicaltrials.gov/study/NCT07282665clinicaltrials.gov· Posted Sep 20, 2026· Starts Dec 11, 2028 ✓· 100% of score
ClinicalTrials.gov lists 2028-12-11 as the estimated primary completion date; a sponsor's estimate, and trials of this size routinely slip.
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