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

The study will be conducted in 2 phases: Phase 2 and Phase 3. In the Part A Phase 2 segment, up to 2,000 participants will be randomly assigned to receive a single injection of either mRNA-1345 vaccine at the selected dose or placebo in a 1:1 randomization ratio. In the Part A Phase 3 segment, approximately 35,000 participants will be randomly assigned to receive a single injection of either mRNA-1345 vaccine at the selected dose or placebo in a 1:1 randomization ratio. In the Part B substudy, 1500 participants who received a dose of mRNA-1345 in Part A Phase 3 will be randomly assigned in a 2:1 randomization ratio to receive a single BD injection of either mRNA-1345 at the selected dose or placebo.