Efficacy Study: This randomized, double-blinded, placebo-controlled Phase 3 study is designed to assess the safety, immunogenicity, and efficacy of a single dose of RSVpreF in the prevention of LRTI-RSV in adults: * At a dose of 120µg. * In adults 60 years of age and older. * The duration of the study for each participant will be up to approximately 24 months. * The study will be conducted in the United States, Canada, Netherlands, Finland, Argentina, Japan and South Africa. Substudy A: This study is an extension of the efficacy study and was designed to evaluate the safety and immunogenicity of a second dose of RSVpreF when administered after a dosing interval of approximately 2 years: * At a dose of 120µg (as studied in the Phase 3 Efficacy Study) * Blood samples will be collected for antibody testing. * The duration of the study for each participant will be up to approximately 18 months. * The study will be conducted in the United States and Argentina. Substudy B: This study was designed to evaluate the safety and immunogenicity of a second dose of RSVpreF when administered after a dosing interval of approximately 1 year: * At a dose of 120µg (as studied in the Phase 3 Efficacy Study) * Blood samples will be collected for antibody testing. * The duration of the study for each participant will be up to approximately 18 months. * The study will be conducted in Argentina. Substudy C: This study was designed to evaluate the safety and immunogenicity of a second dose of RSVpreF when administered after a dosing interval of either 3 or 4 years: * At a dose of 120µg (as studied in the Phase 3 Efficacy Study) * Participants will receive either placebo or a second dose of RSVpreF approximately 3 or 4 years after receiving the initial dose of RSVpreF in the main efficacy study. * Blood samples will be collected for antibody testing. * The duration of the study for each participant will be up to approximately 24 months. * The study will be conducted in the United States and Canada.