Comparative immunogenicity of mRNA-1273 and BNT162b2 SARS-CoV-2 bivalent booster vaccines in US nursing home...

Nursing home residents (NHRs) remain among the most vulnerable to severe outcomes from SARS-CoV-2 infection. While mRNA-1273 (Spikevax, Moderna) and BNT162b2 (Comirnaty, Pfizer-BioNTech) vaccines are widely used in this population, comparative data on their immunogenicity, particularly after bivalent boosters, remain limited. We conducted a longitudinal immunologic evaluation of U.S. NHRs who received either the mRNA-1273 or BNT162b2 bivalent vaccine. Serum samples were collected 10-30 d post-vaccination. Anti-spike IgG levels were measured using a Luminex bead-based assay, and neutralizing titers were assessed via pseudovirus neutralization. Comparative analyses of the titer distributions were performed using two-sided Wilcoxon rank-sum tests. Both vaccine groups demonstrated strong humoral responses to the ancestral Wuhan strain and Omicron BA.4/5 subvariants. Spike-binding antibody levels and neutralization titers were comparable between the mRNA -1273 and BNT162b2 vaccine formulations. Conclusions: Both mRNA-1273 and BNT162b2 mRNA vaccines elicit similarly robust humoral immunity in NHRs, supporting their interchangeable use in booster strategies. Our findings underscore the importance of timely booster administration over exact product selection in protecting this high-risk, immunosenescent population.