A small observational study from Finland adds evidence that maternal Tdap vaccination, while protecting newborns, can dampen children's own antibody responses to the primary DTaP vaccine series. Among preschoolers, those whose mothers received Tdap during pregnancy had significantly lower levels of pertussis and diphtheria antibodies at age 3 and again at age 4, before their scheduled booster.
The gap closed after the age-4 DTaP booster. Children of vaccinated mothers reached anti-pertussis toxin IgG concentrations of 247 IU/mL, compared with 270 IU/mL in children of unvaccinated mothers, a difference the authors describe as immunologic parity. Diphtheria antibody levels also rose to similar levels in both groups.
The findings, published in the Journal of Infectious Diseases, come from an extension of the Finnish MIFI trial. The researchers note that maternal Tdap remains a safe and effective way to protect young infants, who face the highest risk of severe pertussis. They suggest alternatives such as a pertussis-only maternal vaccine or moving the preschool booster earlier, but Lori Handy of Children's Hospital of Philadelphia cautioned that changing the U.S. schedule would require evidence of clinical differences and more population-level data.
Study limitations include the small sample size and loss of participants during follow-up. The authors also observed that children of vaccinated mothers had higher cord-blood antibody levels at birth, confirming the transfer of maternal antibodies.