Moderna Vaccine mRNA-1345 Observational Respiratory Syncytial Virus (RSV) Study

Inclusion Criteria: P901 inclusion criteria: * Must be a participant in P301 * Must be based in the US * Must provide informed consent for P901 P301 key inclusion criteria: * Adults 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 and chronic obstructive pulmonary disease) but should be medically stable in the opinion of the investigator. * Body mass index from ≥18 kilograms (kg)/square meter (m\^2) to ≤35 kg/m\^2. Exclusion Criteria: P901 exclusion criteria: * Receipt of any future licensed RSV vaccine at baseline. * Receipt of any future licensed RSV vaccines during the study follow-up period will result in censorship on the date the vaccine was received. All inclusion and exclusion criteria from P301 that are available in the RWD will be applied to the RWD controls, if built. P301 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.