Study of a Respiratory Syncytial Virus/Human Metapneumovirus Vaccine Candidate

Inclusion Criteria: * Aged 60 years or older on the day of inclusion * A female participant is eligible to participate if she is not pregnant or breastfeeding and is of non-childbearing potential. * Participants who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion Note: Participants with pre-existing stable disease, defined as disease not requiring significant change in therapy or hospitalization for worsening disease during the 6 weeks before enrollment, can be included. Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply: * Any screening laboratory parameter with laboratory abnormalities deemed clinically significant by the investigator * Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive therapy. Persons living with stable human immunodeficiency virus (HIV) are not excluded * Known systemic hypersensitivity to any of the study intervention components (eg, polyethylene glycol, polysorbate); history of a life-threatening reaction to the study interventions used in the study or to a product containing any of the same substances; any allergic reaction (eg, anaphylaxis) after administration of mRNA coronavirus disease 2019 (COVID-19) vaccine * History of RSV and/or hMPV-associated illness, diagnosed clinically, serologically, or microbiologically in the last 12 months * Previous history of myoca…