Citation

Objective: Long-term data on immune responses in children exposed to in-pregnancy tetanus, diphtheria, acellular pertussis (Tdap) vaccination is lacking. This study investigated humoral and cellular immune responses of 5-6-year-old children born to Tdap vaccinated women.

Study design: Within a Belgian cohort study (NCT01698346), long-term follow-up of infants born to in-pregnancy Tdap (Boostrix®) vaccinated women (vaccine group, N=43) or not (control group N=15) was performed. According to national recommendations, children were vaccinated with an aP containing vaccine (DTaP-IPV; Tetravac® or Tetrarix®) in the first year of primary school. Children were sampled before (around 5 years of age) and one month after the booster dose. Tdap-specific immunoglobulins G (IgG) and Pertussis Toxin (PT)-specific T lymphoblast and cytokine responses were evaluated with an in-house bead-based multiplex immunoassay multiplex and a flow cytometric assay, respectively.

Results: At 5 years of age (before DTaP-IPV vaccination), low pertussis toxin (PT), pertactin (Prn), filamentous hemagglutinin, tetanus toxoid, and diphtheria toxoid antibodies were observed in most children, with only Prn antibodies significantly lower in the control group. At this timepoint, all children of the control group but only 63% of the children in the vaccine group were identified as PT-specific CD3+CD4+ lymphoblast responders. DTaP-IPV vaccination significantly increased antibody and T lymphoblast responses in both groups. However, differences between the vaccine and control group remained, as higher CD3+CD8+ lymphoblast populations and IFN-γ cytokine secretions were detected in the control group.

Conclusions: Slight differences in long-term pertussis-specific cellular immune responses were observed in children born to Tdap vaccinated women, suggesting that in-pregnancy vaccination might influence the infants’ immune-priming and might have a long-term impact on the child’s immune responses. More research regarding the possible effects of maternal antibodies on the infant’s immune-priming and its clinical relevance is certainly needed.