The effect of preexisting antibodies from Tdap vaccination during pregnancy on infant antibody responses to the pertussis-containing vaccines

Tetanus-diphtheria-acellular pertussis (Tdap) vaccination during pregnancy protects newborns from pertussis in the early months of life. Previous research indicated that Tdap vaccination during pregnancy may blunt <i>Bordetella pertussis</i> (<i>B. pertussis)</i>-specific antibody responses in infants following acellular (aP) and whole cell pertussis (wP) vaccination. However, the effect of preexisting antibodies on infants' responses to diphtheria toxoid (DT), tetanus toxoid (TT) and <i>B. pertussis</i> antigens is less well-understood. This study aims to quantify the effect of preexisting anti-DT, anti-TT, and <i>B. pertussis</i>-specific antibody levels from Tdap vaccination during pregnancy on infants' post-primary and post-booster responses to aP- and wP-containing vaccines. This retrospective analysis utilized data collected from a randomized controlled trial (NCT02408926) between 2015 and 2018. Pregnant women received Tdap vaccination between 27 and 36 weeks gestation. Their term infants were randomized to receive either a pentavalent DTwP-HB-Hib (wP) or a hexavalent DTaP-HB-Hib-IPV (aP) vaccine. Preexisting immunity was defined as the levels of anti-DT, anti-TT, anti-pertussis toxin (PT), anti-filamentous hemagglutinin (FHA), and anti-pertactin (PRN) IgG at month 2 (pre-vaccination). Blood samples were collected at birth, month 2, month 7 (following primary series vaccination at 2, 4, 6 months), month 18 (pre-booster), and month 19 (post booster). A total of 132 aP-vaccinated and 123 wP-vaccinated children completed this study. High levels of pre-vaccination antibody levels correlated with lower geometric mean ratios (GMRs) at post-primary and post-booster following wP- and aP-containing vaccination. This effect was observed consistently across all vaccine antigens following primary and booster doses. The clinical significance of this observation requires further investigation.