A Study to Evaluate the Safety and Efficacy of mRNA-1345 Vaccine Targeting Respiratory Syncytial Virus (RSV) in Adults ≥60 Years of Age

The main purpose of Part A of this study is to evaluate the safety and tolerability of mRNA-1345 vaccine and to demonstrate the efficacy of a single dose of mRNA-1345 vaccine in the prevention of a first episode of RSV-associated lower respiratory tract disease (RSV-LRTD) as compared with placebo from 14 days postinjection through 12 months. The main purpose of Part B of this study is to evaluate the safety, tolerability and immunogenicity of a booster dose (BD) of mRNA-1345 administered 24 months after the primary dose.