Clostridium Difficile Vaccine Efficacy Trial

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.

• Biological: Clostridium difficile vaccine
  Toxoid-based Clostridium difficile vaccine
• Biological: Placebo
  Normal saline solution (0.9% sodium chloride)

• Experimental: Clostridium difficile vaccine
  Intervention: Biological: Clostridium difficile vaccine
• Placebo Comparator: Placebo
  Intervention: Biological: Placebo

Inclusion Criteria:

• 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.

Exclusion Criteria:

• 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