Maternal RSV vaccination generates high-affinity antibodies that efficiently transfer to infants, providing enhanced passive immunity.

Respiratory syncytial virus (RSV) remains the leading cause of hospitalization in young children. A bivalent pre-fusion (preF) protein RSV vaccine was licensed for pregnant persons in 2023 (Abrysvo, Pfizer), but the impact of RSV maternal immunization on maternal-fetal immunity has not been well characterized. We analyze neutralizing antibody responses, binding antibodies, and antibody affinity maturation in 58 unvaccinated and 49 vaccinated pregnant individuals and their infants. Maternal RSV vaccination induces robust neutralizing antibodies against both RSV-A2 and RSV-B1 strains, with geometric mean titers 8-fold and 13.4-fold higher, respectively, in vaccinated versus unvaccinated participants. Vaccination significantly enhances binding antibodies to RSV-preF protein (5.2-fold higher) and antibody affinity maturation (3.7-fold higher). High-quality RSV-specific antibodies are efficiently transferred across the placenta. However, early preterm infants showed reduced antibody transfer efficiency compared with full-term infants. These findings demonstrate that maternal RSV vaccination generates high-quality, affinity-matured transferable antibodies that provide passive immunity to infants.