Neutralization of BA.4–BA.5, BA.4.6, BA.2.75.2, BQ.1.1, and XBB.1 with Bivalent Vaccine

This clinical letter compares neutralizing antibody responses in adults ≥55 years after receiving a fourth dose of either the original BNT162b2 monovalent vaccine or the updated BA.4–BA.5 bivalent booster. Using live-virus FRNT50 assays, the study evaluated neutralization efficiency against multiple omicron sublineages: BA.4–BA.5, BA.4.6, BA.2.75.2, BQ.1.1, and XBB.1. The bivalent booster consistently elicited stronger immune responses across all tested variants, especially BA.4–BA.5–derived strains (BQ.1.1, XBB.1). The greatest GMFI ratios were observed in participants without prior SARS-CoV-2 infection. Findings support enhanced breadth and immunogenicity of the bivalent booster and reinforce the importance of variant-specific vaccine updates.

This clinical letter compares neutralizing antibody responses in adults ≥55 years after receiving a fourth dose of either the original BNT162b2 monovalent vaccine or the updated BA.4–BA.5 bivalent booster. Using live-virus FRNT50 assays, the study evaluated neutralization efficiency against multiple omicron sublineages: BA.4–BA.5, BA.4.6, BA.2.75.2, BQ.1.1, and XBB.1. The bivalent booster consistently elicited stronger immune responses across all tested variants, especially BA.4–BA.5–derived strains (BQ.1.1, XBB.1). The greatest GMFI ratios were observed in participants without prior SARS-CoV-2 infection. Findings support enhanced breadth and immunogenicity of the bivalent booster and reinforce the importance of variant-specific vaccine updates.