This Phase 2b, multicenter, randomized, placebo-controlled study will evaluate the safety, tolerability, and immunogenicity of a respiratory syncytial virus stabilized prefusion F subunit vaccine (RSV vaccine) in 650 pregnant participants who receive either one of 2 dose levels of the vaccine, formulated with or without aluminum hydroxide, or placebo, as well as assess safety and characteristics of transplacentally transferred antibodies in their infants.