A Study of mRNA-1345 Vaccine Targeting Respiratory Syncytial Virus (RSV) in Adults ≥50 Years of Age

The main purposes of Part A of this study are to evaluate the safety, tolerability, and immunogenicity of mRNA-1345 coadministered with a seasonal influenza vaccine (Afluria® Quadrivalent); to evaluate the impact of coadministered influenza vaccine on the immune response to RSV-A; and to evaluate the impact of coadministered RSV vaccine on the immune response to influenza. The main purposes of Part B of this study are to evaluate the safety, tolerability, and immunogenicity of mRNA-1345 coadministered with mRNA-1273.214; to evaluate the effect of coadministered mRNA-1273.214 on the immune response to RSV-A; and to evaluate the effect of coadministered RSV vaccine on the immune response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The main purposes of Part C (single arm, open-label) of this study are to evaluate the safety and tolerability of a booster dose (BD) of mRNA-1345 administered at 1 Year following a primary dose; to evaluate the immune response to RSV-A of a BD of mRNA 1345 administered at 1 Year following a primary dose; and to evaluate the immune response to RSV-B of a BD of mRNA-1345 administered at 1 Year following a primary dose.