A Study to Evaluate a Modified RNA Vaccine Against Influenza in Adults 18 Years of Age or Older

This is a Phase 3, randomized, observer-blinded study to evaluate the efficacy, safety, tolerability, and immunogenicity of a quadrivalent influenza modRNA vaccine (qIRV) encoding HA of 4 seasonally recommended strains (2 A strains and 2 B strains) compared to licensed quadrivalent influenza vaccine (QIV) in healthy adults 18 years of age and older. Participants may be enrolled in either the reactogenicity subset, immunogenicity subset, or both/neither subset(s). Efficacy will be assessed in this study through surveillance for influenza-like illness.