Clinical Trials

Inclusion Criteria:

• Evidence of a personally signed and dated ICD indicating that the subject has been informed of all pertinent aspects of the study.
• Willing and able to comply with scheduled visits, vaccination plan, and other study procedures.
• 50 Years or older at enrollment.
• Subjects with an increased risk of future contact with healthcare systems by virtue of:
  • At least 1 inpatient hospitalization ≥ 2 nights’ duration in the previous 12 months; or
  • At least 2 emergency room visits in the previous 12 months; or
  • At least 10 outpatient visits (primary and/or secondary care visits; defined as an in-person visit to the office/clinic of a prescribing healthcare provider for the purposes of the diagnosis, treatment, or ongoing management of a medical condition, excluding pharmacy and mental health visits) in the previous 12 months; or
  • Residence in a skilled nursing facility (a residential institution that provides professional nursing care and rehabilitation services, usually following discharge from the hospital); or
  • Residence in a nursing home (a residential institution that provides assistance with activities of daily living); or
  • Inpatient hospitalization ≥ 2 nights’ duration scheduled ³37 days after randomization; or subjects who have received systemic (ie, oral or injected) antibiotics for a minimum of 48 hours at any time in the previous 12 weeks.
• Ability to be contacted by telephone during study participation.
• Negative urine pregnancy test for female subjects of childbearing potential.
• Female subjects of nonchildbearing potential must meet at least 1 of the following criteria:
• Achieved postmenopausal status, defined as follows: cessation of regular menses for at least 12 consecutive months with no alternative pathological or physiological cause; status may be confirmed with a serum follicle-stimulating hormone (FSH) level confirming the postmenopausal state;
  • Have undergone a documented hysterectomy and/or bilateral oophorectomy;
  • Have medically confirmed ovarian failure.
• All other female subjects (including female subjects with tubal ligations) are considered to be 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 Visit 5 (1 month after the third vaccination).
• Previous administration of an investigational C difficile vaccine or C difficile mAb therapy.
• Prior episode of CDI, confirmed by either laboratory test or diagnosis of pseudomembranous colitis at colonoscopy, at surgery, or histopathologically.
• Receipt of blood products or immunoglobulins within 6 months before enrollment.
• Subjects who may be unable to respond to vaccination because of:
  • Metastatic malignancy; or
• • End-stage renal disease (glomerular filtration rate < 15 mL/min/1.73 ^2 or on dialysis); or
  • Any serious medical disorder that in the investigator’s opinion is likely to be fatal within the next 12 months; or
  • Congenital or acquired immunodeficiency; or
• • Receipt of systemic corticosteroids (≥ 20 mg/day of prednisone or equivalent) 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 (does not include appendectomy).
• Any condition or treatment resulting in frequent diarrhea (≥ 3 loose stools per day more than once per month), as reported by the subject.
• Other acute or chronic medical or psychiatric condition including recent (within the past year) or active suicidal ideation or behavioral or laboratory abnormality that may increase the risk associated with study participation or investigational product administration or may interfere with the interpretation of study results and, in the judgment of the investigator, would make the subject inappropriate for entry into this study.
• Pregnant female subjects; breastfeeding female subjects; fertile male subjects and female subjects of childbearing potential who are, in the opinion of the investigator, sexually active and at risk for pregnancy with their partner(s) and are unwilling or unable to use 2 highly effective methods of contraception as outlined in this protocol from the signing of the informed consent until at least 28 days after the last dose of investigational product.