This study is testing the Clostridioides difficile (or C. difficile) vaccine for people aged 65 and older to see if it can reduce infections. Participants will get either the vaccine or a placebo (a harmless shot with no active ingredients). The vaccine is given as a shot in the upper arm.

The goal is to see how many people get diarrhea due to C. difficile. The study could last up to three and a half years, but it might end sooner if results are clear. Participants will have three clinic visits and three phone calls, plus yearly visits after that.

If a participant has three or more loose stools in one day, they must save the next stool and contact the study site. The team will check if it's a C. difficile infection. This can be done at the clinic or via phone or video call.

• The study may last up to 3.5 years with several visits.
• Participants receive either the vaccine or a placebo.
• Participants must report certain symptoms for evaluation.