A Study to Investigate the Immunogenicity and Safety of mRNA COVID-19 Variant-containing Formulations

Inclusion Criteria: * ≥65 years of age at the time of signing the informed consent OR ≥12 to \<65 years of age at the time of signing the informed consent with at least 1 risk factor for severe outcomes from COVID-19. * Female participants of childbearing potential may be enrolled in the study if not pregnant or breastfeeding, subject to other criteria specified in the study protocol. Exclusion Criteria: * History of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection within 6 months prior to enrollment. * Acutely ill or febrile within 72 hours prior to or at Day 1. * History of a diagnosis or conditions that in the Investigator's opinion could affect participant's safety, assessment of endpoints, assessment of immune response, or adherence to study procedures. * Reported history of congenital or acquired immunodeficiency, immunosuppressive condition, asplenia, or recurrent severe infections. * History of coagulopathy or bleeding disorder that is considered a contraindication to IM injection or phlebotomy. * Receipt of any of the following: * COVID-19 vaccine within 6 months prior to enrollment, * Any licensed non COVID-19 vaccine within 28 days before or planned receipt within 28 days after the study intervention, except an influenza vaccine, which may be given 14 days before or after receipt of the study intervention, * Systemic immunosuppressive treatment within 180 days prior to the Screening or is anticipating the need for systemic immunosuppressive treatment at any time during participation in the study, * Systemic immunoglobulins, long-acting biological therapies that affect immune responses, or blood products within 90 days prior to the Day 1 Visit or plans for receipt during the study. Note: Additional protocol-defined inclusion/exclusion criteria may apply.