Trial · NCT03918629

Clostridium Difficile Vaccine 2-Dose Versus 3-Dose Study

NCT03918629, Phase 3, Completed, Pfizer; results first posted 2024-01-10

3 sourcestrials-2026-11-12-0.5.0

Cite this record

ConductScience Library. Clostridium Difficile Vaccine 2-Dose Versus 3-Dose Study. Trials, record NCT03918629. Release trials-2026-11-12-0.5.0, 12 Nov 2026. https://conductscience.org/library/trials/NCT03918629

On this page

Trial

As registered on ClinicalTrials.gov, in the graph's capture of the registry.

Title: Clostridium Difficile Vaccine 2-Dose Versus 3-Dose Study
NCT number: NCT03918629
Status: Completed
Phases: Phase 3
Enrollment: 1,994 participants, actual
Lead sponsor: Pfizer
Conditions: Clostridium Difficile Associated Disease
Interventions: Clostridium difficile, Placebo
First posted: 2019-04-17
Last updated: 2024-01-10
Results first posted: 2024-01-10

Source ClinicalTrials.gov

Registered outcomes12

Each outcome the trial registered, primary first, in ClinicalTrials.gov's words.

List	Outcome	Time frame	Description
Primary	Adjusted Geometric Mean Concentration (GMC) of Clostridium Difficile Toxin A and Toxin B Specific Neutralizing Antibodies at Month 7 for Evaluable Immunogenicity Population (EIP)	Month 7	Adjusted GMCs and 2-sided 95% confidence intervals (CIs) of toxin A and toxin B specific neutralizing antibody levels were calculated by exponentiating the least square (LS) means and the corresponding CIs based on analysis of logarithmically transformed concentrations using a linear regression model with terms of baseline concentration (log scale) and vaccine group. EIP at Month 7 (EI7): all enrolled participants who received all 3 doses of investigational product; had blood drawn for assay testing within 28 to 47 days after visit 4; had valid and determinate assay results for either toxin A or B for the specified analysis at Month 7; had no major protocol deviations.
Primary	Percentage of Participants Achieving Seroresponse for Clostridium Difficile Toxin A and Toxin B at Month 7 for EIP	Month 7	Seroresponse was defined as at least a 4-fold rise from the baseline neutralizing antibody level following vaccination. 95% CI was based on Clopper-Pearson method. EI7: all enrolled participants who received all 3 doses of investigational product; had blood drawn for assay testing within 28 to 47 days after visit 4; had valid and determinate assay results for either toxin A or B for the specified analysis at Month 7; had no major protocol deviations.
Primary	Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 1	Up to 7 days after Dose 1 of investigational product at Month 0	Local reactions included pain at injection site, redness and swelling. These were recorded by participants in an electronic diary (e-diary). Redness and swelling were measured and recorded in measuring device units, where 1 measuring device unit= 0.5 centimeter (cm). Redness and swelling were graded as mild: 2.5-5.0 cm, moderate: greater than (\>) 5.0-10.0 cm, severe: \>10.0 cm, potentially life threatening: necrosis or exfoliative dermatitis for redness, or necrosis for swelling. Pain at injection site was graded as mild: did not interfere with daily activity, moderate: interfered with daily activity, severe: prevented daily activity, potentially life threatening: emergency room visit or hospitalization. The maximum severity was defined as highest grading of each local reaction through 7 days of vaccination.
Primary	Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 2	Up to 7 days after Dose 2 of investigational product at Month 1	Local reactions included pain at injection site, redness and swelling. These were recorded by participants in an e-diary. Redness and swelling were measured and recorded in measuring device units, where 1 measuring device unit= 0.5 cm. Redness and swelling were graded as mild: 2.5-5.0 cm, moderate: \>5.0-10.0 cm, severe: \>10.0 cm, potentially life threatening: necrosis or exfoliative dermatitis for redness, or necrosis for swelling. Pain at injection site was graded as mild: did not interfere with daily activity, moderate: interfered with daily activity, severe: prevented daily activity, potentially life threatening: emergency room visit or hospitalization. The maximum severity was defined as highest grading of each local reaction through 7 days of vaccination.
Primary	Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 3	Up to 7 days after Dose 3 of investigational product at Month 6	Local reactions included pain at injection site, redness and swelling. These were recorded by participants in an e-diary. Redness and swelling were measured and recorded in measuring device units, where 1 measuring device unit= 0.5 cm. Redness and swelling were graded as mild: 2.5-5.0 cm, moderate: \>5.0-10.0 cm, severe: \>10.0 cm, potentially life threatening: necrosis or exfoliative dermatitis for redness, or necrosis for swelling. Pain at injection site was graded as mild: did not interfere with daily activity, moderate: interfered with daily activity, severe: prevented daily activity, potentially life threatening: emergency room visit or hospitalization. The maximum severity was defined as highest grading of each local reaction through 7 days of vaccination.
Primary	Percentage of Participants With Systemic Events by Maximum Severity Through 7 Days After Dose 1	Up to 7 days after Dose 1 of investigational product at Month 0	Systemic events included fever, fatigue, headache, joint pain, muscle pain and vomiting. These were recorded by participants in an e-diary. Fever was categorized as: mild (38.0 to 38.4 degree \[deg\] Celsius \[C\]), moderate (38.5 to 38.9 deg C), severe (39.0 to 40.0 deg C) and potentially life threatening (\>40.0 deg C). Fatigue, headache, muscle pain and joint pain were graded as mild: did not interfere with activity, moderate: some interference with activity, severe: prevented daily routine activity and potentially life threatening: emergency room visit or hospitalization. Vomiting was graded as mild: 1 to 2 times in 24 hours(h), moderate: \>2 times in 24h, severe: required intravenous hydration and potentially life threatening: emergency room visit or hospitalization for hypotensive shock. The maximum severity was defined as highest grading of each systemic event through 7 days of vaccination.
Primary	Percentage of Participants With Systemic Events by Maximum Severity Through 7 Days After Dose 2	Up to 7 days after Dose 2 of investigational product at Month 1	Systemic events included fever, fatigue, headache, joint pain, muscle pain and vomiting. These were recorded by participants in an e-diary. Fever was categorized as: mild (38.0 to 38.4 deg C), moderate (38.5 to 38.9 deg C), severe (39.0 to 40.0 deg C) and potentially life threatening (\>40.0 deg C). Fatigue, headache, muscle pain and joint pain were graded as mild: did not interfere with activity, moderate: some interference with activity, severe: prevented daily routine activity and potentially life threatening: emergency room visit or hospitalization. Vomiting was graded as mild: 1 to 2 times in 24h, moderate: \>2 times in 24h, severe: required intravenous hydration and potentially life threatening: emergency room visit or hospitalization for hypotensive shock. The maximum severity was defined as highest grading of each systemic event through 7 days of vaccination.
Primary	Percentage of Participants With Systemic Events by Maximum Severity Through 7 Days After Dose 3	Up to 7 days after Dose 3 of investigational product at Month 6	Systemic events included fever, fatigue, headache, joint pain, muscle pain and vomiting. These were recorded by participants in an e-diary. Fever was categorized as: mild (38.0 to 38.4 deg C), moderate (38.5 to 38.9 deg C), severe (39.0 to 40.0 deg C) and potentially life threatening (\>40.0 deg C). Fatigue, headache, muscle pain and joint pain were graded as mild: did not interfere with activity, moderate: some interference with activity, severe: prevented daily routine activity and potentially life threatening: emergency room visit or hospitalization. Vomiting was graded as mild: 1 to 2 times in 24h, moderate: \>2 times in 24h, severe: required intravenous hydration and potentially life threatening: emergency room visit or hospitalization for hypotensive shock. The maximum severity was defined as highest grading of each systemic event through 7 days of vaccination.
Primary	Percentage of Participants With Adverse Events Through 1 Month After Last Study Vaccination	From day of first dose up to 1 month after last dose (up to Month 7)	An AE was any untoward medical occurrence in a participant who received investigational product without regard to possibility of causal relationship. Percentage of participants with any AEs (both serious and all non-serious AEs) and non-serious AEs through 1 month after last study vaccination were reported in this outcome measure. Only AEs and non-SAEs collected by non-systematic assessment (i.e., excluding local reactions and systemic events) were reported in this outcome measure.
Primary	Percentage of Participants With Serious Adverse Events (SAEs) Through 6 Months After Last Study Vaccination	From day of first dose up to 6 months after last dose (up to Month 12)	SAE was any untoward medical occurrence that at any dose resulted in any of the following outcomes or deemed significant for any other reason: death; initial or prolonged inpatient hospitalization; life-threatening experience (immediate risk of dying); persistent or significant disability/incapacity; congenital anomaly.

1 to 10 of 12Source ClinicalTrials.gov

See all 12 registered outcomes

Outcomes12

Each outcome the trial posted results for, in ClinicalTrials.gov's words.

Type	Outcome	Time frame	Population	Units	Measured as
PRIMARY	Adjusted Geometric Mean Concentration (GMC) of Clostridium Difficile Toxin A and Toxin B Specific Neutralizing Antibodies at Month 7 for Evaluable Immunogenicity Population (EIP)	Month 7	EI7 population. All participants reported under 'Number of Participants Analyzed' contributed data to the table; however, may not have evaluable data for every row. Number Analyzed signifies participants with valid and determinate assay results for the specified assay at both baseline and the given sampling time point.	Neutralization units per milliliter	GEOMETRIC_MEAN
PRIMARY	Percentage of Participants Achieving Seroresponse for Clostridium Difficile Toxin A and Toxin B at Month 7 for EIP	Month 7	EI7 population. All participants reported under 'Number of Participants Analyzed' contributed data to the table; however, may not have evaluable data for every row. Number Analyzed signifies participants with valid and determinate assay results for the specified assay at both baseline and the given sampling time point.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 1	Up to 7 days after Dose 1 of investigational product at Month 0	Safety analysis set included all participants who received at least 1 dose of the investigational product. Here, Overall Number of Participants Analyzed signifies participants evaluable for this outcome measure.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 2	Up to 7 days after Dose 2 of investigational product at Month 1	Safety analysis set included all participants who received at least 1 dose of the investigational product. Here, Overall Number of Participants Analyzed signifies participants evaluable for this outcome measure.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 3	Up to 7 days after Dose 3 of investigational product at Month 6	Safety analysis set included all participants who received at least 1 dose of the investigational product. Here, Overall Number of Participants Analyzed signifies participants evaluable for this outcome measure.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Systemic Events by Maximum Severity Through 7 Days After Dose 1	Up to 7 days after Dose 1 of investigational product at Month 0	Safety analysis set included all participants who received at least 1 dose of the investigational product. Here, Overall Number of Participants Analyzed signifies participants evaluable for this outcome measure.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Systemic Events by Maximum Severity Through 7 Days After Dose 2	Up to 7 days after Dose 2 of investigational product at Month 1	Safety analysis set included all participants who received at least 1 dose of the investigational product. Here, Overall Number of Participants Analyzed signifies participants evaluable for this outcome measure.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Systemic Events by Maximum Severity Through 7 Days After Dose 3	Up to 7 days after Dose 3 of investigational product at Month 6	Safety analysis set included all participants who received at least 1 dose of the investigational product. Here, Overall Number of Participants Analyzed signifies participants evaluable for this outcome measure.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Adverse Events Through 1 Month After Last Study Vaccination	From day of first dose up to 1 month after last dose (up to Month 7)	Safety analysis set included all participants who received at least 1 dose of the investigational product.	Percentage of participants	NUMBER
PRIMARY	Percentage of Participants With Serious Adverse Events (SAEs) Through 6 Months After Last Study Vaccination	From day of first dose up to 6 months after last dose (up to Month 12)	Safety analysis set included all participants who received at least 1 dose of the investigational product.	Percentage of participants	NUMBER

1 to 10 of 12Source ClinicalTrials.gov

See all 12 outcomes

Results by group238

Each measurement the trial posted, group by group, in the words and numbers it posted.

Outcome	Group	Category	Value	Spread	Units
Adjusted Geometric Mean Concentration (GMC) of Clostridium Difficile Toxin A and Toxin B Specific Neutralizing Antibodies at Month 7 for Evaluable Immunogenicity Population (EIP)	2-Dose Clostridium Difficile Vaccine	Toxin A	693.0	95% Confidence Interval 646.5 to 742.9	Neutralization units per milliliter
Adjusted Geometric Mean Concentration (GMC) of Clostridium Difficile Toxin A and Toxin B Specific Neutralizing Antibodies at Month 7 for Evaluable Immunogenicity Population (EIP)	3-Dose Clostridium Difficile Vaccine	Toxin A	845.7	95% Confidence Interval 789.5 to 906.0	Neutralization units per milliliter
Adjusted Geometric Mean Concentration (GMC) of Clostridium Difficile Toxin A and Toxin B Specific Neutralizing Antibodies at Month 7 for Evaluable Immunogenicity Population (EIP)	2-Dose Clostridium Difficile Vaccine	Toxin B	4166.2	95% Confidence Interval 3759.7 to 4616.7	Neutralization units per milliliter
Adjusted Geometric Mean Concentration (GMC) of Clostridium Difficile Toxin A and Toxin B Specific Neutralizing Antibodies at Month 7 for Evaluable Immunogenicity Population (EIP)	3-Dose Clostridium Difficile Vaccine	Toxin B	7342.9	95% Confidence Interval 6633.1 to 8128.5	Neutralization units per milliliter
Percentage of Participants Achieving Seroresponse for Clostridium Difficile Toxin A and Toxin B at Month 7 for EIP	2-Dose Clostridium Difficile Vaccine	Toxin A	32.2	95% Confidence Interval 28.9 to 35.5	Percentage of participants
Percentage of Participants Achieving Seroresponse for Clostridium Difficile Toxin A and Toxin B at Month 7 for EIP	3-Dose Clostridium Difficile Vaccine	Toxin A	33.9	95% Confidence Interval 30.6 to 37.3	Percentage of participants
Percentage of Participants Achieving Seroresponse for Clostridium Difficile Toxin A and Toxin B at Month 7 for EIP	2-Dose Clostridium Difficile Vaccine	Toxin B	56.7	95% Confidence Interval 53.1 to 60.2	Percentage of participants
Percentage of Participants Achieving Seroresponse for Clostridium Difficile Toxin A and Toxin B at Month 7 for EIP	3-Dose Clostridium Difficile Vaccine	Toxin B	73.5	95% Confidence Interval 70.3 to 76.5	Percentage of participants
Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 1	2-Dose Clostridium Difficile Vaccine	Pain at injection site: Mild	19.1	95% Confidence Interval 16.7 to 21.7	Percentage of participants
Percentage of Participants With Local Reactions by Maximum Severity Through 7 Days After Dose 1	3-Dose Clostridium Difficile Vaccine	Pain at injection site: Mild	17.5	95% Confidence Interval 15.2 to 20.0	Percentage of participants

1 to 10 of 238Source ClinicalTrials.gov

See all 238 results by group

Participant flow12

How many started, completed or left each group, period by period.

Period	Milestone	Group	Participants
Overall Study	STARTED	2-Dose Clostridium Difficile Vaccine	996
Overall Study	STARTED	3-Dose Clostridium Difficile Vaccine	998
Overall Study	Vaccinated With Dose 1	2-Dose Clostridium Difficile Vaccine	994
Overall Study	Vaccinated With Dose 1	3-Dose Clostridium Difficile Vaccine	997
Overall Study	Vaccinated With Dose 2	2-Dose Clostridium Difficile Vaccine	961
Overall Study	Vaccinated With Dose 2	3-Dose Clostridium Difficile Vaccine	964
Overall Study	Vaccinated With Dose 3	2-Dose Clostridium Difficile Vaccine	897
Overall Study	Vaccinated With Dose 3	3-Dose Clostridium Difficile Vaccine	917
Overall Study	COMPLETED	2-Dose Clostridium Difficile Vaccine	863
Overall Study	COMPLETED	3-Dose Clostridium Difficile Vaccine	880

1 to 10 of 12Source ClinicalTrials.gov

See all 12 participant flow

Adverse events470

Each adverse event the trial posted, group by group: the participants affected out of those at risk.

Type	Event	Organ system	Group	Affected	At risk
other	Diarrhoea	Gastrointestinal disorders	2-Dose Clostridium Difficile Vaccine	18	994
other	Diarrhoea	Gastrointestinal disorders	3-Dose Clostridium Difficile Vaccine	21	997
other	Nausea	Gastrointestinal disorders	2-Dose Clostridium Difficile Vaccine	12	994
other	Nausea	Gastrointestinal disorders	3-Dose Clostridium Difficile Vaccine	14	997
other	Vomiting (VOMITING)	Gastrointestinal disorders	2-Dose Clostridium Difficile Vaccine	37	994
other	Vomiting (VOMITING)	Gastrointestinal disorders	3-Dose Clostridium Difficile Vaccine	45	997
other	Fatigue	General disorders	2-Dose Clostridium Difficile Vaccine	13	994
other	Fatigue	General disorders	3-Dose Clostridium Difficile Vaccine	5	997
other	Fatigue (FATIGUE)	General disorders	2-Dose Clostridium Difficile Vaccine	426	994
other	Fatigue (FATIGUE)	General disorders	3-Dose Clostridium Difficile Vaccine	461	997

1 to 10 of 470Source ClinicalTrials.gov

See all 470 adverse events

Adverse event totals6

The totals the trial posted for each group.

Total	Group	Affected	At risk
Total, all-cause mortality	2-Dose Clostridium Difficile Vaccine	15	994
Total, all-cause mortality	3-Dose Clostridium Difficile Vaccine	7	997
Total, other adverse events	2-Dose Clostridium Difficile Vaccine	721	994
Total, other adverse events	3-Dose Clostridium Difficile Vaccine	751	997
Total, serious adverse events	2-Dose Clostridium Difficile Vaccine	141	994
Total, serious adverse events	3-Dose Clostridium Difficile Vaccine	136	997

Source ClinicalTrials.gov

Papers0

The papers the trial lists on ClinicalTrials.gov.

None in this release.

Grants0

The grants NIH RePORTER links to the trial, newest funded first: NIH's, and some of AHRQ's, CDC's, FDA's and VA's. Each shows its title, principal investigators, organization and funder in its newest year.

None in this release.

Trial comparisons2

Comparisons of the trial's two groups, calculated by ConductScience from the counts it posted.

Comparison	Source
2-Dose Clostridium Difficile Vaccine vs 3-Dose Clostridium Difficile Vaccine: deaths from any cause	Trial comparisons
2-Dose Clostridium Difficile Vaccine vs 3-Dose Clostridium Difficile Vaccine: serious adverse events	Trial comparisons

Tests0

The ConductCognition tests this trial's registered outcomes name, as ScienceGraph matched them in trial-tests-2026-11-12-0.2.1.

None in this release.

Data dates

The day each source was copied for this release.

ClinicalTrials.gov: 2026-11-12; ClinicalTrials.gov
Results, from AACT: 2026-03-23; AACT
NIH grant links: 2026-11-13; NIH RePORTER

Sources 3

ClinicalTrials.gov's posted results, through CTTI's AACTFreely available. Acknowledgement requested
ClinicalTrials.govNo license stated
NIH RePORTER's clinical studies and project filesPublic domain

Each source's terms

ClinicalTrials.gov's posted results, through CTTI's AACTClinicalTrials.gov data via Aggregate Analysis of ClinicalTrials.gov (AACT), CTTI. CTTI makes its materials freely available and requests acknowledgement. https://aact.ctti-clinicaltrials.org/documentation/299
ClinicalTrials.govnone stated
NIH RePORTER's clinical studies and project filesPublic domain (NIH RePORTER)

ClinicalTrials.gov's data carry an international copyright outside the United States: https://clinicaltrials.gov/about-site/terms-conditions.

For software

Read this trial from software.

The record and each of its lists are JSON, twenty rows a page. No key.

GET https://conductscience.org/api/trials/v1/NCT03918629

GET https://conductscience.org/api/trials/v1/NCT03918629/results?page=2

API reference For AI assistants