Symptomatic PCR-confirmed CDI cases were defined as the number of participants with combination of clinical and laboratory findings. Clinical components were: >= 3 loose stools in <= 24 hours, loose stools (defined as type 6 [fluffy pieces with ragged edges, mushy] or type 7 [watery, no solid pieces] according to the Bristol Stool Chart) lasting >= 24 hours. Laboratory findings were: stool sample positive for C. difficile Toxin B by PCR at central laboratory or diagnosis of pseudomembranous colitis visualized at colonoscopy.

Analysis was performed on modified intent-to-treat (mITT) population which included all participants who received at least 1 injection and were analyzed according to the group to which they were randomized.

Severe CDI cases were defined as number of participants with at least one of the following symptoms: fever >= 38.5 degree Celsius (°C), white blood cell count >= 15,000 cells/mm^3, ileus, pseudomembranous colitis, serum albumin <3 gram per deciliter, abdominal distension, abdominal tenderness, or admission to the intensive care unit within 7 days of CDI diagnosis.

Analysis was performed on participants with protocol-defined (PCR confirmed) primary CDI cases.

Loose stools were defined as type 6 (fluffy pieces with ragged edges, mushy) or type 7 (watery, no solid pieces) according to the Bristol Stool Chart. In this outcome measure, participants with number of loose stool episodes (categorized as: loose stool episodes less than 3, 3 to 6, 7 to 10, 11 to 15 and greater than 15) were reported.

Analysis was performed on participants with protocol-defined PCR confirmed CDI cases.

Symptomatic PCR confirmed CDI cases were defined as the number of participants with combination of clinical and laboratory findings. Clinical components were: >= 3 loose stools in <= 24 hours, loose stools (defined as type 6 [fluffy pieces with ragged edges, mushy] or type 7 [watery, no solid pieces] according to the Bristol Stool Chart) lasting >= 24 hours. Laboratory findings were: stool sample positive for C. difficile Toxin B by PCR at central laboratory or diagnosis of pseudomembranous colitis visualized at colonoscopy. Analysis was performed on per-protocol efficacy analysis set (PPEAS).

PPEAS: participants who had at least 1 injection, no relevant protocol deviations (not meet inclusion criteria/ met exclusion criteria, not receive any vaccine/not received in proper time window, received different vaccine than randomized, preparation and / or administration of vaccine not done per protocol, received protocol-restricted therapy).

Serum antibody concentrations against toxins A and B were measured by ELISA and expressed as geometric mean concentration (GMC). The 2-sided 95% Confidence Interval (CI) of GMC was based on the Student t-distribution. Analysis was performed on Per Protocol Immunogenicity Analysis Set, which included participants who had at least 1 injection, no relevant protocol deviations (not met inclusion criteria/ met exclusion criteria, not received vaccine/ not received in proper time window, received different vaccine than randomized, preparation and/ or administration of vaccine not per protocol, protocol-restricted therapy, not provided post-dose serology sample/serology sample did not produced a valid test result).

Analysis was performed on Per Protocol Immunogenicity Analysis Set. Here, 'number analyzed' = participants with available data for each specified category.

Percentage of Participants with >= 2 and 4-fold rise in serum antibody concentrations against toxins A and B were measured by ELISA. The 2-sided 95% Cl of the percentage was based on Exact method calculations.

Analysis was performed on Per Protocol Immunogenicity Analysis Set. Here, 'overall number of participants analyzed' = participants evaluable for this outcome measure and 'number analyzed' = participants with available data for each specified category.

Serum antibody concentrations against toxins A and B were measured by ELISA and expressed as GMC. The 2-sided 95% CI GMC was based on the Student t-distribution. Symptomatic PCR-confirmed CDI cases were defined as the number of participants with combination of clinical and laboratory findings. Clinical components were: >= 3 loose stools in <= 24 hours, loose stools (defined as type 6 [fluffy pieces with ragged edges, mushy] or type 7 [watery, no solid pieces] according to the Bristol Stool Chart) lasting >= 24 hours. Laboratory findings were: stool sample positive for C. difficile Toxin B by PCR at central laboratory or diagnosis of pseudomembranous colitis visualized at colonoscopy.

Analysis was performed on participants with protocol-defined (PCR confirmed) primary CDI cases. Here, 'number analyzed' = participants with available data for each specified category.

Serum antibody concentrations against toxins A and B were measured by TNA and expressed as geometric mean titer (GMT). The 2-sided 95% Cl of GMT was based on the Student t-distribution.

Analysis was performed on Per Protocol Immunogenicity Analysis Set. Here, 'number analyzed' = participants with available data for each specified category.

Percentage of Participants with >= 2 and 4-fold rise in serum antibody concentrations against toxins A and B were measured by TNA. The 2-sided 95% CI of the percentage was based on Exact method calculations.

Analysis was performed on Per Protocol Immunogenicity Analysis Set. Here, "overall number of participants analyzed" signifies participants evaluable for this outcome measure and 'number analyzed' = participants with evaluable data for each specified category.

Serum antibody concentrations against toxins A and B were measured by TNA and were expressed as GMT. The 2-sided 95% CI GMC was based on the Student t-distribution. Symptomatic PCR confirmed CDI cases were defined as the number of participants with combination of clinical and laboratory findings. Clinical components were: >= 3 loose stools in <= 24 hours, loose stools (defined as type 6 [fluffy pieces with ragged edges, mushy] or type 7 [watery, no solid pieces] according to the Bristol Stool Chart) lasting >= 24 hours. Laboratory findings were: stool sample positive for C. difficile Toxin B by PCR at central laboratory or diagnosis of pseudomembranous colitis visualized at colonoscopy.

Analysis was performed on participants with protocol-defined (PCR confirmed) primary CDI cases. Here, 'number analyzed' = participants with available data for each specified category.

Solicited injection site reactions: pain, erythema, and swelling. Pain: Grade 1: no interference with activity, Grade 2: some interference with activity, Grade 3: significant; prevents daily activity; Erythema and swelling: Grade 1: >= 25 to <=50 mm, Grade 2: >51 to <=100 mm, Grade 3: >100 mm. Solicited systemic reactions: fever, headache, malaise, myalgia, and arthralgia. Fever: Grade 1: >= 38.0°C to <=38.4°C or >= 100.4° Fahrenheit (F) to <=101.1°F, Grade 2: >=38.5°C to <= 38.9°C or >=101.2°F to <=102.0°F, Grade 3: >=39.0°C or >=102.1°F. Headache, malaise, and myalgia: Grade 1: no interference with activity, Grade 2: some interference with activity, Grade 3: significant; prevents daily activity; Arthralgia: Grade 1: free range of motion but complains of pain or discomfort, Grade 2: decreased range of motion due to pain or discomfort, Grade 3: unwilling to move due to pain.

Analysis was performed on all participants who received vaccine and were evaluable for reactogenicity. Here, 'number analyzed' = participants with available data for each specified category.