This is the Phase 1/2 first-in-human, randomized, placebo-controlled, observer-blinded study evaluating the investigational multivalent group B streptococcus vaccine. Healthy adults aged 18 to 49 years of age with no history of group B streptococcal vaccination will be randomized to receive either a single intramuscular dose of multivalent group B streptococcus vaccine (various formulations at 3 dose levels) or a placebo (saline control).