Additional Study Information: Clostridioides difficile (C. difficile) is a bacterium (germ) that can spread from one person to another causing severe diarrhea (watery poop) that at its worst can lead to death. Pfizer has been studying an investigational vaccine to prevent diarrhea caused by C. difficile. To be part of this study you must be 65 years old or older and have one or more of the risk factors for getting C. difficile diarrhea. Some of these risk factors are one (1) hospitalization for two (2) nights or longer; at least two (2) emergency room visits or at least ten (10) outpatient visits in the last 12 months; received oral or injected antibiotics for two (2) days or longer in the past 12 weeks or 3 months. If you are enrolled into the study, you would have some tests, procedures, and assessments done. You would also need to complete an e-diary, and a diarrhea e-diary, as well as send stool samples to the sponsor. You will also need to visit the study teams clinic at least 5 times during the study and will also need to speak to the study team on the phone for other visits and to check how you are doing. You will receive 2 injections over a period of 6 months. Half of the people in the study will receive the study vaccine, and half will receive a placebo (salt-water). To find out whether the vaccine prevents C. difficile diarrhea, you would be closely monitored for signs of infection for up to 3 years after receiving the last vaccine. You will receive compensation for being part of this study.