Vaccines
STERILE, VIRUS, INFLUENZA
In Part 1, participants received mRNA-1010 or placebo (normal saline), while in Part 2, participants received mRNA-1010 or a licensed standard dose quadrivalent influenza vaccine (Afluria). mRNA-1010 includes mRNAs encoding for the surface glycoprotein HA of four influenza virus strains formulated in lipid nanoparticles. In Part 1, mRNA-1010 encoded influenza strains recommended by the WHO for 2020-2021 SH cell- or recombinant-based vaccines (see Supplementary Methods for details). In Part 2, mRNA-1010 encoded strains recommended by the WHO for 2021–2022 NH cell- or recombinant-based vaccines (see Supplementary Methods for details). mRNA-1010 was provided as a sterile liquid for injection and diluted to different dose levels with normal saline. All vaccines were administered intramuscularly as a single 0.5-mL injection.