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 myocarditis, pericarditis, and/or myopericarditis * Screening electrocardiogram that is consistent with possible myocarditis, pericarditis, and/or myopericarditis or, in the opinion of the investigator, demonstrates clinically relevant abnormalities that may affect participant safety or study results * Thrombocytopenia or bleeding disorder, contraindicating intramuscular (IM) injection based on investigator's judgment * Receipt of anticoagulants in the 3 weeks preceding inclusion * Chronic illness that, in the opinion of the investigator, is at a stage where it might interfere with study conduct or completion * Alcohol, prescription drug, or substance abuse that, in the opinion of the investigator, might interfere with the study conduct or completion * History of acute infection symptoms or a positive severe acute respiratory syndrome coronavirus reverse transcription polymerase chain reaction (SARS-CoV-2 RT-PCR) or antigen test in the 10 days prior to the visit. A prospective participant should not be included in the study until the condition has resolved * Receipt of any vaccine other than mRNA vaccine in the 4 weeks preceding any study intervention administration or planned receipt of any vaccine other than mRNA vaccine in the 4 weeks following any study intervention administration * Receipt of any mRNA vaccine in the 60 days preceding any study intervention administration or planned receipt of any mRNA vaccine in the 60 days following any study intervention administration * Previous vaccination against RSV and/or hMPV (with a licensed or investigational vaccine either as a monovalent vaccine or any combination of the antigens) * Receipt of immune globulins, blood, or blood-derived products in the past 3 months * Participation at the time of study enrollment (or in the 4 weeks preceding the first study intervention administration) or planned participation during the present study period in another clinical study investigating a vaccine, drug, medical device, or medical procedure The above information is not intended to contain all considerations relevant to a potential participation in a clinical trial.