Clostridoides Difficile Associated DiseasePhase 1/2NCT05805826
To Understand the Safety and Effects of a C. Difficile Vaccine With New Adds-Ons That Will Be Given to Healthy Adults
A Phase 1/2 study testing C. difficile vaccine (previously studied formulation)., C. difficile vaccine formulation 1. and C. difficile vaccine formulation 2. in people with Clostridoides Difficile Associated Disease, run by Pfizer at 23 sites in United States.
Trial summary
An antibody is a substance your body makes to fight off infection. This study will explore the safety and antibody response of a vaccine to prevent severe diarrhea caused by a germ called Clostridoides difficile (C. diff). Three new formulations of the C. diff vaccine will be used in this study, in addition to a C. Read more about this study
- Who is it for?
- Ages 50 years and olderHealthy volunteers can take part
- Conditions the study is for
- Clostridoides Difficile Associated Disease
- What is being tested?
- C. difficile vaccine (previously studied formulation)., C. difficile vaccine formulation 1. and C. difficile vaccine formulation 2.
- Type of treatment
- Vaccines, Injection or infusion
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 936 participants
- Where
- 23 sitesUnited States
- Study dates
- 23 Mar 2023to 19 Jun 2031
- Phase
- Phase 1/2
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 50 years and older
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- Each phase of the study will enroll participants in different age categories:
- Phase 1: Participants ≥65 to <85 years of age; Phase 2: Participants ≥65 years of age; Cohort 4 Participants 50 through 64 years of age.
- Healthy participants as determined by medical history, clinical assessment, and the judgment of the investigator.
- Participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures.
- Capable of giving personally signed informed consent, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.
Who cannot join
- Fertile male participants and WOCBP who are unwilling or unable to use an effective method of contraception from the signing of informed consent until at least 28 days after the last dose of study intervention.
- Serious chronic disorder, including history of metastatic malignancy, severe COPD requiring supplemental oxygen, end-stage renal disease with or without dialysis, cirrhosis of the liver, clinically unstable cardiac disease, or any other disorder that, in the investigator's opinion, would make the participant inappropriate for entry into the study.
- Any contraindication to vaccination or vaccine components, including previous hypersensitivity or anaphylactic reaction to any vaccine or vaccine-related components.
- Prior episode of CDI, confirmed by either laboratory test or diagnosis of pseudomembranous colitis at colonoscopy, at surgery, or histopathologically.
- Any bleeding disorder or anticoagulant therapy that would contraindicate intramuscular injection.
- Known or suspected immunodeficiency or other conditions associated with immunosuppression, including, but not limited to, leukocyte, lymphocyte, or immunoglobulin class/subclass deficiencies or abnormalities, generalized malignancy, HIV infection, leukemia, lymphoma, or organ or bone marrow transplant.
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- Other medical or psychiatric condition including recent (within the past year) or active suicidal ideation/behavior or laboratory abnormality that may increase the risk of study participation or, in the investigator's judgment, make the participant inappropriate for the study.
- Previous receipt of an investigational C difficile vaccine or C difficile mAb therapy.
- Receipt of blood product or immunoglobulin within 6 months before enrollment.
- Currently receives treatment with immunosuppressive therapy, including cytotoxic agents or systemic corticosteroids, or planned receipt throughout the study. Participants may not be enrolled if corticosteroids were administered within 28 days before study intervention administration.
- Participation in other studies involving investigational drugs, investigational vaccines, or investigational devices within 28 days prior to study entry through 12 months after the last dose of study intervention.
- Phase 1 only: Any screening hematology and/or blood chemistry laboratory value that meets the definition of a ≥ Grade 1 abnormality.
- Investigator site staff directly involved in the conduct of the study and their family members, site staff otherwise supervised by the investigator, and sponsor and sponsor delegate employees directly involved in the conduct of the study and their family members.
Trial locations and contacts
23 sites in 1 country.
23 sites in 1 country
United States23 sites
Anaheim Clinical Trials, LLC
Anaheim, California, 92801
Benchmark Research
Austin, Texas, 78705
Great Lakes Clinical Trials - Ravenswood
Chicago, Illinois, 60640
CTI Clinical Research Center
Cincinnati, Ohio, 45212
Alliance for Multispecialty Research, LLC
Doral, Florida, 33172
Qcare Site Services Inc. d/b/a Avacare
Durham, North Carolina, 27703
Indago Research & Health Center, Inc
Hialeah, Florida, 33012
Research Centers of America
Hollywood, Florida, 33024
Miami Clinical Research
Miami, Florida, 33155
New Horizon Research Center
Miami, Florida, 33165
Charisma Medical and Research Center
Miami Lakes, Florida, 33014
NYU Langone Health
New York, New York, 10016
Private Practice - Dr. Hector Fabregas
Pembroke Pines, Florida, 33026
DBC Research USA
Pembroke Pines, Florida, 33029
HOPE Research Institute
Phoenix, Arizona, 85032
BRCR Medical Center Inc.
Plantation, Florida, 33322
Rochester Clinical Research, Inc.
Rochester, New York, 14609
Prism Research LLC dba Nucleus Network
Saint Paul, Minnesota, 55114
Washington University School of Medicine
St Louis, Missouri, 63110
Washington University
St Louis, Missouri, 63130
Clinical Research Trials of Florida
Tampa, Florida, 33607
Dynamed Clinical Research, LP d/b/a DM Clinical Research
Tomball, Texas, 77375
Alliance for Multispecialty Research, LLC
Wichita, Kansas, 67226
About this study
Official title: A PHASE 1/2 RANDOMIZED STUDY TO EVALUATE THE SAFETY, TOLERABILITY, IMMUNOGENICITY, AND IMMUNOPERSISTENCE OF A CLOSTRIDIOIDES DIFFICILE VACCINE ADMINISTERED WITH NOVEL ADJUVANTS IN HEALTHY ADULTS
An antibody is a substance your body makes to fight off infection. This study will explore the safety and antibody response of a vaccine to prevent severe diarrhea caused by a germ called Clostridoides difficile (C. diff). Three new formulations of the C. diff vaccine will be used in this study, in addition to a C. diff vaccine formulation that has been studied in previous clinical trials.
The purpose of this study is to understand if giving the new C. diff vaccine formulations helps people make as many antibodies as giving the previously studied C. diff vaccine formulation.
Read more
The study is divided into 2 phases.
Phase 1 will evaluate 3 new formulations of the C. diff vaccine and 2 dosing schedules spread out over 2 months or 6 months.
The Phase 1 portion of the study is seeking participants:
- who are healthy adults of 65 to 84 years of age
- who have not had a C. diff infection before
- who have not received a C. diff vaccine or C. diff monoclonal antibody therapy before.
All participants in Phase 1 will receive study injections with active vaccine or placebo at each vaccination visit, depending on the vaccine group to which they are assigned. A placebo does not contain any active ingredients. Participants in Phase 1 will attend at least 9 study visits and will take part in the study for approximately 18 months. Based on the results of Phase 1, 1 or 2 of the new C. diff vaccine formulations will be chosen for further study in Phase 2.
Phase 2 will evaluate the safety and effects of the new C. diff vaccine formulation(s) chosen in Phase 1.
The Phase 2 portion of the study is seeking participants:
- who are healthy adults ≥65 years of age; and 50 through 64 years of age (Cohort 4 only)
- who have not had a C. diff infection before
- who have not received a C. diff vaccine or C. diff monoclonal antibody therapy before.
Phase 2 participants will receive active C. diff vaccine or placebo at each vaccination visit. Participants in Phase 2 will attend at least 6 and up to 12 study visits and will take part in the study for up to 4 years.
A booster stage for selected participants in Phase 2 will have participants receive active C. diff vaccine or placebo to examine immune persistence. The booster stage participants will attend at least 10 additional study visits and will take part in the study for 6 years.
A newly added cohort will evaluate the safety and effects of active C. diff vaccine formulation in participants 50 through 64 years of age. Participants will receive C. diff vaccine or placebo and will attend at least 6 study visits over a period of 18 months.
- Being tested
- C. difficile vaccine (previously studied formulation)., C. difficile vaccine formulation 1., C. difficile vaccine formulation 2., C. difficile vaccine formulation 3., Saline Placebo.
- Keywords
- Clostridioides difficile, Clostridium difficile, C. diff, Persistence, Vaccine, Cohort
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
C. difficile vaccine (previously studied formulation).Biological
Toxoid based Clostridioides difficile vaccine (previously studied formulation) given as an intramuscular injection
C. difficile vaccine formulation 1.Biological
- difficile vaccine formulation 1 given as an intramuscular injection
C. difficile vaccine formulation 2.Biological
- difficile vaccine formulation 2 given as an intramuscular injection
C. difficile vaccine formulation 3.Biological
- difficile vaccine formulation 3 given as an intramuscular injection
Saline Placebo.Other
0.9% sodium chloride solution given as an intramuscular injection
| Study group | Role | What they receive |
|---|---|---|
| C. difficile vaccine formulation 1, Schedule 2 (Phase 1) | Experimental | Novel vaccine formulation 1 Receives: Biological: C. difficile vaccine formulation 1.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 3 (Phase 1) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 3, Schedule 2 (Phase 1) | Experimental | Novel vaccine formulation 3 Receives: Biological: C. difficile vaccine formulation 3.; Other: Saline Placebo. |
| C. difficile vaccine formulation 1, Schedule 4 (Phase 1) | Experimental | Novel vaccine formulation 1 Receives: Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 4 (Phase 1) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 3, Schedule 4 (Phase 1) | Experimental | Novel vaccine formulation 3 Receives: Biological: C. difficile vaccine formulation 3.; Other: Saline Placebo. |
| C. difficile vaccine (previously studied formulation) Schedule 1 (Phase 1) | Active comparator | Previously studied C. difficile vaccine formulation Receives: Biological: C. difficile vaccine (previously studied formulation).; Other: Saline Placebo. |
| C difficile vaccine formulation 2, Schedule 1 (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 4 (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 5 (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 6 (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2. |
| C. difficile vaccine (previously studied formulation) , Schedule 1 (Phase 2) | Active comparator | Previously studied C. difficile vaccine formulation Receives: Biological: C. difficile vaccine (previously studied formulation).; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 7 (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 1, (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2. |
| C. difficile vaccine formulation 2, Schedule 4, (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 8, (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| C. difficile vaccine formulation 2, Schedule 9, (Phase 2) | Experimental | Novel vaccine formulation 2 Receives: Biological: C. difficile vaccine formulation 2.; Other: Saline Placebo. |
| Saline placebo, Schedule 4 (Phase 2) | Placebo comparator | Saline placebo Receives: Other: Saline Placebo. |
What is being measured
The primary outcome is the main question the study is designed to answer.
Phase 1: Percentage of participants reporting local reactions
Injection site pain, redness, and swelling as self-reported in electronic diaries
Measured: For 7 days after each vaccination
Phase 1: Percentage of participants reporting systemic events
Vomiting, diarrhea, headache, fatigue, new or worsening muscle pain, new or worsening joint pain, and fever, as self-reported in electronic diaries
Measured: For 7 days after each vaccination
Phase 1: Percentage of participants reporting adverse events
As elicited by investigational site staff
Measured: From each vaccination through 1 month after vaccination
Phase 1: Percentage of participants reporting serious adverse events
As elicited by investigational site staff
Measured: From Dose 1 (Day 1) through 6 months after the last dose
Phase 1: Percentage of participants reporting medically attended adverse events
As elicited by investigational site staff
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
As measured at the central laboratory
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
Injection site pain, redness, and swelling as self-reported in electronic diaries
Measured: For 7 days after each vaccination
Phase 2: Percentage of participants reporting systemic events
Vomiting, diarrhea, headache, fatigue, new or worsening muscle pain, new or worsening joint pain, and fever, as self-reported in electronic diaries
Measured: For 7 days after each vaccination
Phase 2: Percentage of participants reporting adverse events
As elicited by investigational site staff
Measured: From each dose of study intervention through 1 month after each dose of study intervention
Phase 2: Percentage of participants reporting adverse events
As elicited by investigational site staff
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
As elicited by investigational site staff
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
As elicited by investigational site staff
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
As measured at the central laboratory
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
As measured at the central laboratory
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
As measured at the central laboratory
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
As measured at the central laboratory
Measured: At Month 7 comparing data from ≥65 years of age to data from 50 through 64 years of age
Secondary outcomes (12)
Phase 1: Percentage of participants reporting serious adverse events
As elicited by investigational site
Measured: From 6 months through 12 months after the last dose of study intervention
Phase 1: Percentage of participants reporting medically attended adverse events
As elicited by investigational site
Measured: From 6 months through 12 months after the last dose of study intervention
Phase 1: Geometric mean concentration (GMC) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
As measured at the central laboratory
Measured: 1 month after each dose, before the last dose, 6 months after the last dose, and 12 months after the last dose
Phase 1: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
As measured at the central laboratory
Measured: From before Dose 1 (Day 1) to 1 month after each dose, and to 6 months and 12 months after the last dose
Phase 2: Percentage of participants reporting medically attended adverse events
As elicited by investigational site
Measured: From 6 month through 12 months after the last dose of study intervention
Phase 2: Percentage of participants reporting serious adverse events
As elicited by investigational site
Measured: From 6 month through 12 months after the last dose
Phase 2: Geometric mean concentration (GMT) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
As measured at the central laboratory
Measured: At each planned post vaccination time point
Phase 2: Geometric mean ratio (GMR) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
As measured at the central laboratory
Measured: At each planned post vaccination time point
Phase 2: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
As measured at the central laboratory
Measured: From before vaccination to each planned post vaccination time point
Phase 2: The percentage of participants with a greater than or equal to 4-fold rise in C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
As measured at the central laboratory
Measured: From before vaccination to each planned vaccination time point
Phase 2: Geometric mean concentration (GMT) of C. difficile toxin A- and toxin B- specific neutralizing antibodies
As measured at the central laboratory
Measured: At each planned persistence time point
Phase 2: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B- specific neutralizing antibodies
As measured at the central laboratory
Measured: From before vaccination to each planned persistence time point
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted10 Apr 2023
- Study start23 Mar 2023
- Primary completion19 Jun 2031 (estimated)
- Study completion19 Jun 2031 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Clostridoides Difficile Associated DiseaseStudies of the same condition, open and under way.
- More trials run by PfizerThe sponsor's other registered studies.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 1/2
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Parallel assignment
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 936 participants (actual)
Sponsor and investigators
- Lead sponsor
- Pfizer
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
- Investigators
- Pfizer CT.gov Call Center, Study director, Pfizer
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT05805826
- Sponsor's protocol ID
- C4771001
- Other IDs
- NCT05805826
- Status last verified
- Apr 2026
- First submitted
- 21 Mar 2023
- Last updated
- 29 Apr 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- Yes: Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.
Study at a glance
From the registry record, last updated by the sponsor on 29 Apr 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A PHASE 1/2 RANDOMIZED STUDY TO EVALUATE THE SAFETY, TOLERABILITY, IMMUNOGENICITY, AND IMMUNOPERSISTENCE OF A CLOSTRIDIOIDES DIFFICILE VACCINE ADMINISTERED WITH NOVEL ADJUVANTS IN HEALTHY ADULTS
- ClinicalTrials.gov ID
- NCT05805826
- Acronym / sponsor ID
- C4771001
- Keywords
- Clostridioides difficile, Clostridium difficile, C. diff, Persistence, Vaccine, Cohort
- Phase
- Phase 1/2
- Study type
- Interventional
- Recruitment status
- Active, not recruiting
- Enrolment
- 936 participants (actual)
- Lead sponsor
- PfizerIndustry (pharma, biotech, devices)
- Study start
- 23 Mar 2023 (actual)
- Primary completion
- 19 Jun 2031 (estimated)
- Study completion
- 19 Jun 2031 (estimated)
- First posted
- 10 Apr 2023 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
An antibody is a substance your body makes to fight off infection. This study will explore the safety and antibody response of a vaccine to prevent severe diarrhea caused by a germ called Clostridoides difficile (C. diff). Three new formulations of the C. diff vaccine will be used in this study, in addition to a C. diff vaccine formulation that has been studied in previous clinical trials.
The purpose of this study is to understand if giving the new C. diff vaccine formulations helps people make as many antibodies as giving the previously studied C. diff vaccine formulation.
The study is divided into 2 phases.
Phase 1 will evaluate 3 new formulations of the C. diff vaccine and 2 dosing schedules spread out over 2 months or 6 months.
The Phase 1 portion of the study is seeking participants:
- who are healthy adults of 65 to 84 years of age
- who have not had a C. diff infection before
- who have not received a C. diff vaccine or C. diff monoclonal antibody therapy before.
All participants in Phase 1 will receive study injections with active vaccine or placebo at each vaccination visit, depending on the vaccine group to which they are assigned. A placebo does not contain any active ingredients. Participants in Phase 1 will attend at least 9 study visits and will take part in the study for approximately 18 months. Based on the results of Phase 1, 1 or 2 of the new C. diff vaccine formulations will be chosen for further study in Phase 2.
Phase 2 will evaluate the safety and effects of the new C. diff vaccine formulation(s) chosen in Phase 1.
The Phase 2 portion of the study is seeking participants:
- who are healthy adults ≥65 years of age; and 50 through 64 years of age (Cohort 4 only)
- who have not had a C. diff infection before
- who have not received a C. diff vaccine or C. diff monoclonal antibody therapy before.
Phase 2 participants will receive active C. diff vaccine or placebo at each vaccination visit. Participants in Phase 2 will attend at least 6 and up to 12 study visits and will take part in the study for up to 4 years.
A booster stage for selected participants in Phase 2 will have participants receive active C. diff vaccine or placebo to examine immune persistence. The booster stage participants will attend at least 10 additional study visits and will take part in the study for 6 years.
A newly added cohort will evaluate the safety and effects of active C. diff vaccine formulation in participants 50 through 64 years of age. Participants will receive C. diff vaccine or placebo and will attend at least 6 study visits over a period of 18 months.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Triple blind (participant, investigator, outcomes assessor)
- Number of arms
- 18
- Model description
- Parallel assignment
| Arm | Type | Receives |
|---|---|---|
| C. difficile vaccine formulation 1, Schedule 2 (Phase 1) | Experimental | Biological: C. difficile vaccine formulation 1., Other: Saline Placebo.Novel vaccine formulation 1 |
| C. difficile vaccine formulation 2, Schedule 3 (Phase 1) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 3, Schedule 2 (Phase 1) | Experimental | Biological: C. difficile vaccine formulation 3., Other: Saline Placebo.Novel vaccine formulation 3 |
| C. difficile vaccine formulation 1, Schedule 4 (Phase 1) | Experimental | Other: Saline Placebo.Novel vaccine formulation 1 |
| C. difficile vaccine formulation 2, Schedule 4 (Phase 1) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 3, Schedule 4 (Phase 1) | Experimental | Biological: C. difficile vaccine formulation 3., Other: Saline Placebo.Novel vaccine formulation 3 |
| C. difficile vaccine (previously studied formulation) Schedule 1 (Phase 1) | Active comparator | Biological: C. difficile vaccine (previously studied formulation)., Other: Saline Placebo.Previously studied C. difficile vaccine formulation |
| C difficile vaccine formulation 2, Schedule 1 (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 4 (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 5 (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 6 (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2.Novel vaccine formulation 2 |
| C. difficile vaccine (previously studied formulation) , Schedule 1 (Phase 2) | Active comparator | Biological: C. difficile vaccine (previously studied formulation)., Other: Saline Placebo.Previously studied C. difficile vaccine formulation |
| C. difficile vaccine formulation 2, Schedule 7 (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 1, (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 4, (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 8, (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| C. difficile vaccine formulation 2, Schedule 9, (Phase 2) | Experimental | Biological: C. difficile vaccine formulation 2., Other: Saline Placebo.Novel vaccine formulation 2 |
| Saline placebo, Schedule 4 (Phase 2) | Placebo comparator | Other: Saline Placebo.Saline placebo |
Who may qualify
- Ages
- 50 years and older
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (5 listed)
- Each phase of the study will enroll participants in different age categories:
- Phase 1: Participants ≥65 to <85 years of age; Phase 2: Participants ≥65 years of age; Cohort 4 Participants 50 through 64 years of age.
- Healthy participants as determined by medical history, clinical assessment, and the judgment of the investigator.
- Participants who are willing and able to comply with all scheduled visits, investigational plan, laboratory tests, lifestyle considerations, and other study procedures.
- Capable of giving personally signed informed consent, which includes compliance with the requirements and restrictions listed in the ICD and in this protocol.
Key exclusion criteria (13 listed)
- Fertile male participants and WOCBP who are unwilling or unable to use an effective method of contraception from the signing of informed consent until at least 28 days after the last dose of study intervention.
- Serious chronic disorder, including history of metastatic malignancy, severe COPD requiring supplemental oxygen, end-stage renal disease with or without dialysis, cirrhosis of the liver, clinically unstable cardiac disease, or any other disorder that, in the investigator's opinion, would make the participant inappropriate for entry into the study.
- Any contraindication to vaccination or vaccine components, including previous hypersensitivity or anaphylactic reaction to any vaccine or vaccine-related components.
- Prior episode of CDI, confirmed by either laboratory test or diagnosis of pseudomembranous colitis at colonoscopy, at surgery, or histopathologically.
- Any bleeding disorder or anticoagulant therapy that would contraindicate intramuscular injection.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| C. difficile vaccine (previously studied formulation).Toxoid based Clostridioides difficile vaccine (previously studied formulation) given as an intramuscular injection | Biological | C. difficile vaccine (previously studied formulation) , Schedule 1 (Phase 2), C. difficile vaccine (previously studied formulation) Schedule 1 (Phase 1) |
| C. difficile vaccine formulation 1.C. difficile vaccine formulation 1 given as an intramuscular injection | Biological | C. difficile vaccine formulation 1, Schedule 2 (Phase 1) |
| C. difficile vaccine formulation 2.C. difficile vaccine formulation 2 given as an intramuscular injection | Biological | C difficile vaccine formulation 2, Schedule 1 (Phase 2), C. difficile vaccine formulation 2, Schedule 1, (Phase 2), C. difficile vaccine formulation 2, Schedule 3 (Phase 1), C. difficile vaccine formulation 2, Schedule 4 (Phase 1), C. difficile vaccine formulation 2, Schedule 4 (Phase 2), C. difficile vaccine formulation 2, Schedule 4, (Phase 2), C. difficile vaccine formulation 2, Schedule 5 (Phase 2), C. difficile vaccine formulation 2, Schedule 6 (Phase 2), C. difficile vaccine formulation 2, Schedule 7 (Phase 2), C. difficile vaccine formulation 2, Schedule 8, (Phase 2), C. difficile vaccine formulation 2, Schedule 9, (Phase 2) |
| C. difficile vaccine formulation 3.C. difficile vaccine formulation 3 given as an intramuscular injection | Biological | C. difficile vaccine formulation 3, Schedule 2 (Phase 1), C. difficile vaccine formulation 3, Schedule 4 (Phase 1) |
| Saline Placebo.0.9% sodium chloride solution given as an intramuscular injection | Other | C difficile vaccine formulation 2, Schedule 1 (Phase 2), C. difficile vaccine (previously studied formulation) , Schedule 1 (Phase 2), C. difficile vaccine (previously studied formulation) Schedule 1 (Phase 1), C. difficile vaccine formulation 1, Schedule 2 (Phase 1), C. difficile vaccine formulation 1, Schedule 4 (Phase 1), C. difficile vaccine formulation 2, Schedule 3 (Phase 1), C. difficile vaccine formulation 2, Schedule 4 (Phase 1), C. difficile vaccine formulation 2, Schedule 4 (Phase 2), C. difficile vaccine formulation 2, Schedule 4, (Phase 2), C. difficile vaccine formulation 2, Schedule 5 (Phase 2), C. difficile vaccine formulation 2, Schedule 7 (Phase 2), C. difficile vaccine formulation 2, Schedule 8, (Phase 2), C. difficile vaccine formulation 2, Schedule 9, (Phase 2), C. difficile vaccine formulation 3, Schedule 2 (Phase 1), C. difficile vaccine formulation 3, Schedule 4 (Phase 1), Saline placebo, Schedule 4 (Phase 2) |
Primary outcome
Phase 1: Percentage of participants reporting local reactions
Time frame: For 7 days after each vaccination
Injection site pain, redness, and swelling as self-reported in electronic diaries
Phase 1: Percentage of participants reporting systemic events
Time frame: For 7 days after each vaccination
Vomiting, diarrhea, headache, fatigue, new or worsening muscle pain, new or worsening joint pain, and fever, as self-reported in electronic diaries
Phase 1: Percentage of participants reporting adverse events
Time frame: From each vaccination through 1 month after vaccination
As elicited by investigational site staff
Phase 1: Percentage of participants reporting serious adverse events
Time frame: From Dose 1 (Day 1) through 6 months after the last dose
As elicited by investigational site staff
Phase 1: Percentage of participants reporting medically attended adverse events
Time frame: From Dose 1 (Day 1) through 6 months after the last dose of study intervention
As elicited by investigational site staff
Phase 1: Percentage of participants with abnormal hematology and chemistry laboratory values
Time frame: 1 week after Dose 1 (Day 7) and 1 month after each dose (through Month 7)
As measured at the central laboratory
Phase 2: Percentage of participants reporting local reactions
Time frame: For 7 days after each vaccination
Injection site pain, redness, and swelling as self-reported in electronic diaries
Phase 2: Percentage of participants reporting systemic events
Time frame: For 7 days after each vaccination
Vomiting, diarrhea, headache, fatigue, new or worsening muscle pain, new or worsening joint pain, and fever, as self-reported in electronic diaries
Phase 2: Percentage of participants reporting adverse events
Time frame: From each dose of study intervention through 1 month after each dose of study intervention
As elicited by investigational site staff
Phase 2: Percentage of participants reporting adverse events
Time frame: From the first dose of study intervention through 1 month after the last dose of study intervention
As elicited by investigational site staff
Phase 2: Percentage of participants reporting medically attended adverse events
Time frame: From the first dose of study intervention through 6 months after the last dose of study intervention
As elicited by investigational site staff
Phase 2: Percentage of participants reporting serious adverse events
Time frame: From the first dose of study intervention through 6 months after the last dose of study intervention
As elicited by investigational site staff
Phase 2: Geometric mean concentration (GMT) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
Time frame: 1 month after the last dose of study intervention
As measured at the central laboratory
Phase 2: Geometric mean ratio (GMR) of C. difficile toxin A- and toxin B- specific neutralizing antibodies
Time frame: 1 month after the last dose of study intervention
As measured at the central laboratory
Phase 2: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
Time frame: From before vaccination to 1 month after the last dose
As measured at the central laboratory
Phase 2: Geometric mean ratio (GMR) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
Time frame: At Month 7 comparing data from ≥65 years of age to data from 50 through 64 years of age
As measured at the central laboratory
12 secondary outcomes
Phase 1: Percentage of participants reporting serious adverse events
Time frame: From 6 months through 12 months after the last dose of study intervention
Phase 1: Percentage of participants reporting medically attended adverse events
Time frame: From 6 months through 12 months after the last dose of study intervention
Phase 1: Geometric mean concentration (GMC) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
Time frame: 1 month after each dose, before the last dose, 6 months after the last dose, and 12 months after the last dose
Phase 1: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
Time frame: From before Dose 1 (Day 1) to 1 month after each dose, and to 6 months and 12 months after the last dose
Phase 2: Percentage of participants reporting medically attended adverse events
Time frame: From 6 month through 12 months after the last dose of study intervention
Phase 2: Percentage of participants reporting serious adverse events
Time frame: From 6 month through 12 months after the last dose
Phase 2: Geometric mean concentration (GMT) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
Time frame: At each planned post vaccination time point
Phase 2: Geometric mean ratio (GMR) of C. difficile toxin A- and toxin B-specific neutralizing antibodies
Time frame: At each planned post vaccination time point
Phase 2: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
Time frame: From before vaccination to each planned post vaccination time point
Phase 2: The percentage of participants with a greater than or equal to 4-fold rise in C. difficile toxin A- and toxin B-specific neutralizing antibody concentrations
Time frame: From before vaccination to each planned vaccination time point
Phase 2: Geometric mean concentration (GMT) of C. difficile toxin A- and toxin B- specific neutralizing antibodies
Time frame: At each planned persistence time point
Phase 2: Geometric mean fold-rise (GMFR) of C. difficile toxin A- and toxin B- specific neutralizing antibodies
Time frame: From before vaccination to each planned persistence time point
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 29 Apr 2026.
- To obtain contact information for a study center near you, click here.Link provided by the sponsor.
- Individual participant dataSharing planned: Yes. Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical_trials/trial_data_and_results/data_requests.
Related trials for Clostridoides Difficile Associated Disease
RecruitingPhase 3
A Study to Learn About a Clostridioides Difficile Vaccine in People 65 Years of Age and Older
Clostridoides Difficile Associated Disease
RecruitingPhase 2/3
Secondary Prevention of Clostridioides Difficile Using Vancomycin
Clostridioides Difficile Infection, Clostridioides Difficile Infection Recurrence
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.
Pfizer CT.gov Call Center study director
Pfizer
23 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 1/2 study testing C. difficile vaccine (previously studied formulation)., C. difficile vaccine formulation 1. and C. difficile vaccine formulation 2. in people with Clostridoides Difficile Associated Disease, run by Pfizer at 23 sites in United States.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 5 inclusion and 13 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: under way, not looking for participants, as of the sponsor's last update on 29 Apr 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 23 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this combined phase mean?
Phase 1 studies test a treatment in a small group of people for the first time or in a new way, mainly to check safety and find the right dose.
Phase 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Phase 1: Percentage of participants reporting local reactions (time frame: For 7 days after each vaccination). The study lists 16 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 29 Apr 2026.