Study of a Human Metapneumovirus/Respiratory Syncytial Virus mRNA Vaccine Candidate Encapsulated in a Lipid Nanoparticle-based Formulation in Adults Aged 60 Years and Older

Inclusion Criteria:

• Aged 60 years or older on the day of inclusion

• A female participant is eligible to participate if she is not pregnant orbreastfeeding and is of non-childbearing potential. To be considered ofnon-childbearing potential, a female must be postmenopausal for at least 1 year orsurgically sterile

Exclusion Criteria:

• Any screening laboratory parameter with laboratory abnormality > Grade 1 deemedclinically significant by the investigator

• Known or suspected congenital or acquired immunodeficiency; or receipt ofimmunosuppressive therapy, such as anti-cancer chemotherapy or radiation therapy,within the preceding 6 months; or long-term systemic corticosteroid therapy (prednisone or equivalent for more than 2 consecutive weeks within the past 3months). Of note, persons living with stable human immunodeficiency virus (HIV) arenot excluded

• Known systemic hypersensitivity to any of the study intervention components (eg,polyethylene glycol, polysorbate); history of a life-threatening reaction to thestudy interventions used in the study or to a product containing any of the samesubstances; any allergic reaction (eg, anaphylaxis) after administration of an mRNAvaccine

• History of RSV and/or hMPV-associated illness, diagnosed serologically ormicrobiologically 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 orstudy results

• Laboratory-confirmed thrombocytopenia, contraindicating IM injection, based oninvestigator's judgment

• Bleeding disorder or receipt of anticoagulants in the 3 weeks preceding inclusion,contraindicating IM injection, based on investigator's judgment

• Chronic illness that, in the opinion of the investigator, is at a stage where itmight interfere with study conduct or completion

• Receipt of any vaccine other than mRNA vaccine in the 28 days preceding any studyintervention administration or planned receipt of any vaccine other than mRNAvaccine in the 28 days following any study intervention administration

• Receipt of any mRNA vaccine in the 60 days preceding any study interventionadministration or planned receipt of any mRNA vaccine in the 60 days following anystudy intervention administration

• Previous vaccination against RSV and/or hMPV (with a licensed or investigationalvaccine 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

Note: The above information is not intended to contain all considerations relevant to a potential participation in a clinical trial.