SF2a-TT15 Conjugate Vaccine in Healthy Adult Volunteers

Subjects will be assigned to one of two cohorts. 1. Cohort 1 will receive the lower dose of 2 μg vaccine (with or without alum adjuvant) or matching placebo. 2. Cohort 2 will receive the higher dose of 10 μg vaccine (with or without alum adjuvant) or matching placebo. Eligible subjects will be randomized to receive the 2 μg dose or 10 µg without or with alum or matching placebo, at a ratio of 3:1, as three single IM injections. There will be an interval of 28(±3) days) between each treatment. The study will be conducted in a stepwise approach in which a "Pioneer" Group of 2 subjects (one receiving the active vaccine and one receiving the matching placebo) will receive the first injection. These subjects will remain in-house for a 24-hours medical observation after the first injection (not required in the subsequent injections) Once it has been established that there are no safety concerns in the non-adjuvanted "Pioneer" Groups (and after no less than 48 hrs), the next "Pioneer" group (one subject receiving adjuvanted 2 μg vaccine and one receiving the matching alum placebo) will be injected. If no safety concerns are raised in this group also, after no less than 48 hrs, the rest of the subjects may receive the first injection.