for people ages 50 years and up (full criteria)
healthy people welcome
study started
estimated completion



The Clover trial is evaluating an investigational vaccine that may help to prevent Clostridium difficile infection. Participants in the study are adults 50 years of age and older, who are at risk of developing Clostridium difficile infection. The study will assess whether the vaccine prevents the disease, and whether it is safe and well tolerated. Each subject will receive 3 doses of Clostridium difficile vaccine or placebo and be followed for up to 3 years after vaccination for potential Clostridium difficile infection.

Official Title

A Phase 3, Placebo-controlled, Randomized, Observer-blinded Study To Evaluate The Efficacy, Safety, And Tolerability Of A Clostridium Difficile Vaccine In Adults 50 Years Of Age And Older


Clostridium Difficile Infection Vaccines Clostridium difficile vaccine


You can join if…

Open to people ages 50 years and up

  • Evidence of a personally signed and dated informed consent document.
  • Willing and able to comply with study procedures.
  • Subjects with an increased risk of future contact with healthcare systems or subjects who have received systemic antibiotics in the previous 12 weeks.
  • Ability to be contacted by telephone during study participation.
  • Negative urine pregnancy test for female subjects of childbearing potential.

You CAN'T join if...

  • Investigator site staff members directly involved in the conduct of the study and their family members, site staff members otherwise supervised by the investigator, or subjects who are Pfizer employees, including their family members, directly involved in the conduct of the study.
  • Participation in other studies involving investigational drug(s)/vaccine(s) within 28 days prior to study entry until 1 month after the third vaccination.
  • Previous administration of an investigational C difficile vaccine or C difficile mAb therapy.
  • Prior episode of CDI..
  • Receipt of blood products or immunoglobulins within 6 months before enrollment.
  • Subjects who may be unable to respond to vaccination due to:
  • Metastatic malignancy; or
  • End-stage renal disease; or
  • Any serious medical disorder likely to be fatal within the next 12 months; or
  • Congenital or acquired immunodeficiency; or
  • Receipt of high dose systemic corticosteroids for 14 days within 28 days of enrollment; or
  • Receipt of chronic systemic treatment with other known immunosuppressant medications, or radiotherapy, within 6 months of enrollment.
  • Known infection with human immunodeficiency virus (HIV).
  • Any bleeding disorder or anticoagulant therapy that would contraindicate intramuscular injection.
  • Any contraindication to vaccination or vaccine components, including previous anaphylactic reaction to any vaccine or vaccine-related components.
  • Prior small- or large-bowel resection.
  • Any condition or treatment resulting in frequent diarrhea.
  • Other acute or chronic condition or abnormality that may increase the risk associated with study participation or IP administration or may interfere with interpretation of study results
  • Pregnant or breastfeeding female subjects; male subjects and female subjects who are sexually active and at risk for pregnancy and will not/cannot use 2 methods of contraception


  • Ronald Reagan Med Center - Univeristy of California, Los Angeles (UCLA) accepting new patients
    Los Angeles California 90095 United States
  • Ronald Reagan UCLA Medical Center accepting new patients
    Los Angeles California 90095 United States
  • UCLA CTRC Outpatient Unit accepting new patients
    Los Angeles California 90095 United States
  • University Of California, Davis Medical Center accepting new patients
    Sacramento California 95817 United States
  • VA San Diego Healthcare System accepting new patients
    San Diego California 92161 United States
  • Paradigm Clinical Research Centers, Inc. accepting new patients
    San Diego California 92117 United States
  • Kaiser Permanente Daly City accepting new patients
    Daly City California 94015 United States
  • Kaiser Permanente Vaccine Study Center not yet accepting patients
    Oakland California 94612 United States


accepting new patients
Start Date
Completion Date
To obtain contact information for a study center near you, click here.
Phase 3
Study Type
Last Updated