• Age ≥ 12 years where permitted, and ≥ 18 years in other locations, with a laboratory-confirmed qualifying episode of CDI and at least 1 prior occurrence within the last 6 months

• Age ≥ 75 years with a laboratory-confirmed qualifying episode of CDI

• OR age ≥ 12 years where permitted, and ≥ 18 years in other locations, with least two of the following risk factors:

‣ Age ≥ 65 years

⁃ Kidney dysfunction, defined as estimated creatinine clearance \< 60 mL/min/1.73 m\^2 at the time of the qualifying CDI episode

⁃ History of regular use of a proton pump inhibitor (PPI) within the past 2 months and expectation of continued use of PPIs throughout the study

⁃ History of a prior CDI episode between 6 and 12 months prior to enrollment

⁃ Immunosuppression due to an underlying disease or its treatment

⁃ Has undergone solid organ or hematopoietic stem cell transplantation

• The qualifying episode of CDI must meet all the following criteria:

‣ New onset of ≥ 3 unformed bowel movements (ie, Types 5 to 7 on the Bristol stool scale) within 24 hours for 2 consecutive days

⁃ CDI symptoms started within 4 weeks prior to initiation of standard of care (SoC) antibiotic therapy for CDI

⁃ Stool sample collected before (or no later than 72 hours after) initiation of SoC antibiotic therapy that was positive in a CDI laboratory test, defined as enzyme immunoassay (EIA) for toxin A/B and glutamate dehydrogenase (GDH) with polymerase chain reaction (PCR) reflex testing for discordant EIA/GDH results, performed at either a local laboratory or the central laboratory

⁃ Diarrhea considered unlikely to have another etiology

• Prior to receiving any study medication, the participant should:

‣ Receive and complete a course of SoC antibiotic therapy for at least 10 days, up to a maximum of 28 days (Note: choice of agent is at the physician's discretion and antibiotic tapering is not allowed). It is permissible for decentralized participants to be randomized during SoC antibiotic administration.

⁃ Meet the criterion of a successful clinical response, defined attaining symptomatic control of the qualifying CDI episode, ie, \< 3 loose/unformed bowel movements per 24 hours for at least 2 consecutive days

• Able to receive the first dose of study drug on the last planned day of SoC antibiotic administration for a qualifying CDI episode, or no later than 2 days after completion of antibiotic dosing

• Recovered from any complications of severe or fulminant CDI and be clinically stable by the time of randomization