Study of a Candidate Clostridium Difficile Toxoid Vaccine in Subjects at Risk for C. Difficile Infection

The aim of this study was to evaluate the efficacy of the Clostridium difficile vaccine to prevent primary symptomatic C. difficile infection (CDI) in participants at risk for CDI where there is a substantial unmet medical need. Primary objective: * To assess the efficacy of the C. difficile vaccine in preventing the onset of symptomatic primary CDI confirmed by polymerase chain reaction (PCR) in adult participants aged \>= 50 years who are at risk for CDI and have received at least 1 injection. Secondary Objectives: Efficacy: * To assess prevention of symptomatic PCR-confirmed primary CDI cases after 3 injections administered at 0, 7, and 30 days. * To assess prevention of symptomatic PCR-confirmed primary CDI cases after completion of at least 2 injections. Immunogenicity: * To describe the immunogenicity to toxin A and toxin B at specific time points in a subset of participant and in participants with CDI at Day 0 and Day 60. Safety: * To describe the safety profile of all participants who received at least 1 injection.