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. To be considered of non-childbearing potential, a female must be postmenopausal for at least 1 year or surgically sterile.

• Participants with high-risk medical conditions who are determined by medical history, physical examination (if required), and clinical judgment of the investigator to be eligible for inclusion.

Exclusion Criteria: Participants are excluded from the study if any of the following criteria apply:

• Known or suspected congenital or acquired immunodeficiency; or receipt of immunosuppressive 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 3 months)
• 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 an mRNA vaccine
• History of RSV-associated illness, diagnosed clinically, serologically, or microbiologically in the last 12 months
• Previous history of myocarditis, pericarditis, and/or myopericarditis
• Thrombocytopenia, contraindicating IM injection based on investigator's judgment
• Bleeding disorder or receipt of anticoagulants in the 3 weeks preceding inclusion, contraindicating IM injection
• 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
• Receipt of any vaccine in the 4 weeks preceding any study intervention administration or planned receipt of any 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 with a licensed or investigational vaccine or planned receipt during study participation, of vaccination against RSV with a licensed or investigational vaccine other than the study vaccine
• 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 Note: The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.