Maternal DTaP immunization and transplacental transfer of pertussis antibodies in Japan

BACKGROUND: Maternal pertussis immunization prevents severe infection in early infancy. In Japan, the diphtheria-tetanus-acellular pertussis (DTaP) vaccine is available during pregnancy, whereas the tetanus-diphtheria-acellular pertussis (Tdap) vaccine is not approved. Although they share antigens, DTaP includes higher antigen levels than Tdap. Evidence on maternal DTaP immunization and antibody transfer remains limited. This study evaluated transplacental pertussis antibody transfer after maternal DTaP immunization. METHODS: This single-center observational study included pregnant women who delivered at a tertiary perinatal center (May 2023 and February 2025) classified as antibody-positive (maternal PT-IgG ≥10 EU/mL), unvaccinated (PT-IgG <10 EU/mL without immunization), or vaccinated (PT-IgG <10 EU/mL with DTaP). Maternal and cord blood samples were analyzed for pertussis toxin IgG (PT-IgG) and filamentous hemagglutinin IgG (FHA-IgG). RESULTS: We included 240 women (80/group). Cord blood antibody positivity rates were 70%, 94%, and 14% in the antibody-positive, vaccinated, and unvaccinated groups (P<0.0001). PT-IgG titers were 14.8, 30.0, and 4.41 EU/mL, and FHA-IgG titers were 18.9, 75.3, and 9.52 EU/mL (P<0.0001). Gestational week at immunization and antibody titers were not correlated, and no serious vaccine-related adverse events occurred. CONCLUSIONS: Maternal DTaP immunization demonstrated efficient transplacental transfer. These findings support maternal DTaP use in Japan to enhance neonatal protection against pertussis where Tdap is unavailable.