Study to Evaluate the Safety, Reactogenicity, and Immunogenicity of mRNA-1403 and mRNA-1405 to Prevent Norovirus Acute Gastroenteritis in Healthy Adults 18 to 80 Years of Age

Key Inclusion Criteria: * Part A Phase 1: Adults 18 to 49 years of age at the time of consent or adults 60 to 80 years of age at the time of consent. * Part B Phase 2 and Part C Phase 2: Adults 18 to 80 years of age at the time of consent. * Body mass index of 18 to 39 kilogram/meter\^2 (inclusive) at the Screening Visit. * Participants assigned female at birth are eligible to participate if they are not pregnant or breast/chest/body feeding. * A person of childbearing potential is using a highly effective contraceptive method. * Participant has provided written informed consent for participation in this study. Key Exclusion Criteria: * Is acutely ill or febrile (temperature ≥38.0°C \[100.4°F\]) 72 hours prior to or at the Screening Visit or Day 1. * Part B Phase 2 booster extension period: acute disease or febrile 72 hours prior to or on Day 365. * History of a diagnosis or condition that, in the judgment of the Investigator, is clinically unstable or may affect participant safety, assessment of safety endpoints, assessment of immune response, or adherence to study procedures. * Has a medical, psychiatric, or occupational condition, including reported history of substance abuse, which may pose additional risk as a result of participation, or that could interfere with safety assessments or interpretation of results according to the Investigator's judgment. * Has a current or previous diagnosis of immunosuppressive condition, to include human immunodeficiency virus, or immu…