Mizumaki

Researchers are evaluating the effectiveness, safety, and tolerability of a vaccine designed to reduce Clostridioides difficile C. difficile infections in adults aged 65 years and older. This phase 3 study compares the vaccine to a placebo in a group of older adults who have recent or planned contact with healthcare systems or recent antibiotic use. The purpose is to understand how well the vaccine works to prevent infections and to monitor any side effects or reactions. Participants will receive either the C. difficile vaccine or a placebo shot injected into the upper arm muscle. The study is randomized, double-blinded, and placebo-controlled. The vaccination period includes two doses and participants will be monitored for up to about three and a half years. Follow-up includes three planned clinical visits and three phone visits initially, then yearly clinic visits until the study ends. Participants are asked to report and save stool samples if they experience three or more loose stools in 24 hours to check for possible infection. During the study, researchers will track local and systemic reactions to the vaccine within seven days after each shot, adverse events up to one month after each vaccination, and serious adverse events for up to 18 months after the last dose. The main measurement is the occurrence of medically attended primary C. difficile infections from two weeks after the second vaccination through the surveillance period. Safety monitoring and annual visits will continue until the study is completed, which could be sooner or later depending on infection rates.