Impact of tetanus-diphtheria-acellular pertussis immunization during pregnancy on subsequent infant immunization seroresponses: follow-up from a large randomized placebo-controlled trial.

•Infants of mothers who participated in a phase IV maternal pertussis immunization trial (NCT02377349) received hexavalent DTaP and PCV13 primary series.•High levels of maternally transferred pertussis antibodies persisted in infants from Tdap-vaccinated mothers until 2–3 months after birth.•These maternally transferred pertussis antibodies interfered with the infant immune response to the pertussis components of the primary DTaP series.•The clinical significance of this interference remains unknown.