Humoral Immunogenicity of mRNA-1345 RSV Vaccine in Older Adults

Background The mRNA-1345 vaccine demonstrated efficacy against respiratory syncytial virus (RSV) disease with acceptable safety in adults aged >= 60 years in the ConquerRSV trial. Here, humoral immunogenicity results from the trial are presented.Methods This phase 2/3 trial randomly assigned adults (>= 60 years) to mRNA-1345 50-mu g encoding prefusion F (preF) glycoprotein (n = 17 793) vaccine or placebo (n = 17 748). RSV-A and RSV-B neutralizing antibody (nAb) and preF binding antibody (bAb) levels at baseline and day 29 postvaccination were assessed in a per-protocol immunogenicity subset (PPIS; mRNA-1345, n = 1515; placebo, n = 333).Results Day 29 nAb geometric mean titers (GMTs) increased 8.4-fold against RSV-A and 5.1-fold against RSV-B from baseline. Seroresponses (4-fold rise from baseline) in the mRNA-1345 groups were 74.2% and 56.5% for RSV-A and RSV-B, respectively. Baseline GMTs were lower among participants who met the seroresponse criteria than those who did not. mRNA-1345 induced preF bAbs at day 29, with a pattern similar to nAbs. Day 29 antibody responses across demographic and risk subgroups were generally consistent with the overall PPIS.Conclusions mRNA-1345 enhanced RSV-A and RSV-B nAbs and preF bAbs in adults (>= 60 years) across various subgroups, including those at risk for severe disease, consistent with its demonstrated efficacy in the prevention of RSV disease.Clinical Trials Registration NCT05127434. mRNA-1345 vaccine enhanced levels of RSV-A and RSV-B neutralizing antibody and preF binding antibody compared with placebo in adults (>= 60 years) across various subgroups, including those at risk for severe disease, consistent with its demonstrated efficacy in the prevention of RSV disease.