RecruitingPHASE3INTERVENTIONAL

A Study to Learn About a Clostridioides Difficile Vaccine in People 65 Years of Age and Older

This study is looking at a new vaccine designed to protect against Clostridioides difficile (C. difficile), a type of gut infection. The main goal is to find out how safe and effective this vaccine is at preventing C. difficile infections in people aged 65 and older. Participants will be randomly assigned to receive either the C. difficile vaccine or a 'dummy' shot (placebo), which contains no active medicine. Both are given as injections in the arm. Researchers will be monitoring participants closely for signs of C. difficile infection, particularly severe diarrhoea. Your involvement could last up to three and a half years, including a mix of clinic and phone appointments.

At a glance

Status

Recruiting

Phase

PHASE3

Sponsor

Pfizer

Enrolment target

32,000

Start

10 Dec 2025

Estimated completion

07 Jun 2029

Clostridioides Difficile Associated Disease

What is this study about?

This research study is focused on a new vaccine for a serious gut infection called Clostridioides difficile, often shortened to C. difficile. This infection can cause severe diarrhoea and other health problems, especially in older adults who have recently been in hospital or taken antibiotics.

The main aim of this study is to discover if this new C. difficile vaccine can effectively reduce the number of these infections in people aged 65 and over. We also want to understand if the vaccine is safe and if people can tolerate it well without too many side effects. Participants will receive either the actual vaccine or a placebo, which looks just like the vaccine but doesn't contain any active ingredients.

We will be carefully watching to see how many people in each group develop C. difficile infections. The study length might vary; if many infections happen quickly, it could finish sooner, but if they are rare, it might take a bit longer. Sometimes, the study might even stop early if the vaccine shows a very clear effect, either positive or negative. Your contribution is vital in helping us understand if this vaccine could become a valuable tool in protecting older adults from this infection.

Key takeaways

Tests a new C. difficile vaccine in people aged 65 and older.
Aims to see if the vaccine is safe and prevents infection.
Participants receive either the vaccine or a look-alike dummy shot (placebo).
Study involvement could last up to three and a half years.
Involves a mix of clinic visits and phone check-ups.
Close monitoring for severe diarrhoea, a key symptom of C. difficile.

Who may be eligible?

This study is specifically for people aged 65 and older. You might be a good fit if you've recently been in contact with healthcare services, like visiting a clinic or hospital, or if you've recently taken antibiotics. These situations can sometimes increase the risk of C. difficile.

However, there are some reasons why you might not be able to join. For example, if you've had a C. difficile infection before, or if you've had surgery on your intestines, you wouldn't be eligible. Also, if you tend to have frequent diarrhoea, or if you've already received a C. difficile vaccine or special antibody treatment, this study wouldn't be right for you.

Other reasons that might prevent you from joining include having a serious allergic reaction to past vaccines, having a weakened immune system, or having certain serious health conditions like widespread cancer or kidney failure. The study team will review all your health information to make sure it's safe for you to take part.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

Are you 65 years old or older?
Have you recently been in contact with healthcare or taken antibiotics?
Have you *never* had a C. difficile infection before?
Do you *not* have frequent diarrhoea (more than once a month)?
Have you *not* had any surgery to remove part of your intestines?
Do you *not* have a weakened immune system, widespread cancer, or kidney failure?

Answer every question to see your result.

What does participation involve?

If you decide to take part in this study, you will be in it for up to about three and a half years. You will receive either the C. difficile vaccine or a placebo (a dummy shot with no active medicine) as an injection into your upper arm muscle. Neither you nor the study team will know which one you receive.

Over the course of the study, you'll have three planned clinic visits and three planned phone calls. After these initial visits, you'll have one clinic visit each year until the study ends. You'll also be asked to monitor your health at home. If you experience three or more loose stools (diarrhoea) in a 24-hour period, you should save the next loose stool sample and contact the study team immediately. They will then check for a C. difficile infection, which might involve a visit to the clinic or a phone/video call.

Potential risks and benefits

By taking part, you could potentially help medical science understand if this vaccine can prevent C. difficile infections, which could benefit many older adults in the future. However, there are no guaranteed personal benefits from receiving the vaccine as it might not be effective for everyone, or you might receive the placebo. As with any vaccine, there's a possibility of side effects, such as soreness or redness at the injection site, or more rarely, an allergic reaction. You are free to withdraw from the study at any time, for any reason, without it affecting your medical care.

Locations (174)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

North Alabama Research Center
Verified postcode
Athens, United States· Recruiting
Lakeview Clinical Research
Verified postcode
Guntersville, United States· Recruiting
Medical Affiliated Research Center
Verified postcode
Huntsville, United States· Recruiting
Epic Medical Research-Sun City
Verified postcode
Sun City, United States· Recruiting
Applied Research Center of Arkansas
Verified postcode
Little Rock, United States· Recruiting
Kaiser Permanente Daly City
Verified postcode
Daly City, United States· Recruiting
Kaiser Permanente Los Angeles Medical Center
Verified postcode
Los Angeles, United States· Recruiting
Kaiser Permanente Oncology Pharmacy #014C
Verified postcode
Los Angeles, United States· Recruiting
Sacramento VA Medical Center
Verified postcode
Mather, United States· Not yet recruiting
Kaiser Permanente Oakland
Verified postcode
Oakland, United States· Recruiting
Kaiser Permanente Ontario Medical Center
Verified postcode
Ontario, United States· Recruiting
Southern California Permanente Medical Group
Verified postcode
Pasadena, United States· Recruiting

Common questions

What is C. difficile?

C. difficile (Clostridioides difficile) is a type of germ that can cause a serious infection in your gut, leading to severe diarrhoea.

Why is this study only for people aged 65 and over?

Older adults are more likely to get C. difficile infections, especially after hospital stays or taking antibiotics, so this study focuses on this age group.

What is a 'placebo'?

A placebo is a 'dummy' treatment that looks just like the real vaccine but doesn't contain any active medicine. It helps researchers compare the vaccine's effects.

How will I know if I get the vaccine or the placebo?

Neither you nor the study team will know if you're getting the vaccine or the placebo during the study. This helps keep the results fair and unbiased.

What happens if I get diarrhoea during the study?

If you experience three or more loose stools in 24 hours, you should collect a sample and contact the study team right away. They will check to see if it's C. difficile.

How to find out more

Pfizer CT.gov Call Center

clinicaltrials.gov_inquiries@pfizer.com 1-800-718-1021 Official trial record

Always speak to your GP or specialist before deciding to take part in a study.