Key Inclusion Criteria:  Adults ≥ 60 years of age who are primarily responsible for self-care and activities of daily living. Participants may have one or more chronic medical diagnoses (specifically chronic heart failure [CHF] and chronic obstructive pulmonary disease [COPD]), but should be medically stable as assessed by the following criteria: absence of changes in medical therapy within 1 month due to treatment failure or toxicity; absence of medical events qualifying as SAEs within 1 month of the planned study injection on Day 1; and absence of known, current, and life-limiting diagnoses, which could continue for the duration of the primary efficacy period (12 months from study injection on Day 1) and which, in the opinion of the investigator, would make completion of the protocol unlikely. Body mass index from ≥18 kilograms (kg)/square meter (m^2) to ≤35 kg/m^2.  Key Exclusion Criteria:  Participation in another clinical research study where participant has received an investigational product (drug/biologic/device) within 45 days before the planned date of the Day 1 vaccination. Prior participation in research involving receipt of any investigational RSV product (drug/biologic/device). History of a serious reaction to any prior vaccination or Guillain-Barré syndrome within 6 weeks of any prior influenza immunization. Received or plans to receive any non-study vaccine within 28 days before or after the Day 1 study injection. The exceptions are seasonal influenza vaccines, pneumococcal vaccines, or authorized or approved vaccines for the prevention of COVID-19 (regardless of type of vaccine), which are not permitted within 14 days before or after the Day 1 study injection. Efforts should be made to space study injection and COVID-19 vaccination by at least 7 and preferably 14 days, but COVID-19 vaccination should not be delayed.  Other inclusion and/or exclusion criteria may apply.