Study of a Candidate Clostridium Difficile Toxoid Vaccine in Healthy Adult Subjects Aged 40 to 75 Years in Japan

Participants will be randomly assigned to receive the vaccine or placebo on the selected schedule. Safety parameters, solicited injection site and systemic reactions will be collected for 6 days after each injection; unsolicited adverse events including serious adverse events will be collected up to Day 60 post-vaccination.

Inclusion criteria

• Healthy adult subjects aged 40 to 75 years on the day of inclusion
• Informed consent form has been signed and dated
• Able to attend all scheduled visits and to comply with all trial procedures.

Exclusion criteria

• Subject is pregnant, or lactating, or of childbearing potential (to be considered of non-childbearing potential, a female must be post-menopausal for at least 1 year, surgically sterile, or using an effective method of contraception or abstinence from at least 4 weeks prior to the first vaccination and until at least 4 weeks after the last vaccination)
• Participation in the 4 weeks preceding the first trial vaccination or planned participation during the present trial period in another clinical trial investigating a vaccine, drug, medical device, or medical procedure
• Receipt of any vaccine in the 4 weeks preceding the first trial vaccination, except for influenza (seasonal or pandemic) and pneumococcal vaccine.
• Planned receipt of any vaccine between study vaccinations and in the 4 weeks following the last trial vaccination, except for influenza (seasonal or pandemic) and pneumococcal vaccines
• Previous vaccination against C. difficile with either the trial vaccine another vaccine, or monoclonal antibodies
• Self-reported current or prior Clostridium difficile infection (CDI) episode
• Receipt of blood or blood-derived products in the past 3 months, which might interfere with assessment of the immune response
• Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy such as anti-cancer chemotherapy or radiation therapy within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3 months)
• Self-reported seropositivity for human immunodeficiency virus (HIV), hepatitis B, or hepatitis C
• Known systemic hypersensitivity to any of the vaccine components (including aluminum hydroxide, sodium citrate,sucrose, formaldehyde, sodium chloride), or history of a life-threatening reaction to a vaccine containing any of the same substances
• Known medical history or concomitant disease of thrombocytopenia
• Deprived of freedom by an administrative or court order, or in an emergency setting, or hospitalized involuntarily
• Current alcohol abuse or drug addiction that might interfere with the ability to comply with trial procedures
• Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with trial conduct or completion
• Subjects who have any history of intestinal diverticular bleeding
• Subjects who have had surgery within the past three months for Gastro-Intestinal malignancy
• Moderate or severe acute illness/infection (according to investigator judgment) on the day of vaccination or febrile illness (temperature ≥ 37.5°C). A prospective subject should not be included in the study until the condition has resolved or the febrile event has subsided
• Identified as an Investigator or employee of the Investigator or study center with direct involvement in the proposed study, or identified as an immediate family member (i.e., parent, spouse, natural or adopted child) of the Investigator or employee with direct involvement in the proposed study
• Subject who has concomitant disease that, according to investigator's/sub-investigator's judgment, would adversely affect the safety of the subject in the study, e.g., cardiovascular disease, renal disease, hepatic disease, hematologic disease, and/or growth impairment
• Subject with a past history of convulsions
• Subject ineligible for participation in the study according to the investigator's/sub-investigator's judgment.