The Journal of Infectious Diseases (JID)The Effect of Pertussis Vaccination During Pregnancy on Pertussis and Diphtheria Immunity in Children at 3 and 4 Years of Age

⚠️ Small Study / Early Comparative Evidence

This prospective follow-up examined whether antibody blunting associated with Tdap vaccination during pregnancy persisted beyond infancy. Among children from an earlier Finnish clinical trial, maternal Tdap exposure was associated with lower pertussis toxin and diphtheria IgG concentrations at ages 3 and 4. After the four-year DTaP-IPV booster, antibody concentrations and pertussis toxin-neutralizing titers were comparable between groups. The small cohort and loss to follow-up limit conclusions about clinical protection or vaccination-policy changes.

Clinical Considerations

• At age 3, anti-pertussis toxin IgG was 2.4 versus 5.8 IU/mL in maternal-Tdap and control groups, respectively.
• At age 4 before boosting, anti-pertussis toxin and anti-diphtheria toxin IgG remained significantly lower after maternal Tdap exposure.
• Pertussis seropositivity at age 3 was 21% versus 62%, although no established antibody correlate of protection exists for pertussis.
• Prediphtheria seroprotection was low in both groups, reaching 8% after maternal Tdap exposure and 25% among controls at age 3.
• The preschool booster produced comparable anti-PT, anti-DT, anti-TT, anti-FHA, and neutralizing antibody responses in both groups.
• Interpretation is constrained by small samples, attrition, unadjusted comparisons, pandemic-era exposure patterns, and possible natural boosting during Finland’s 2024 pertussis surge.

Practice Applications

• Recognize that maternal Tdap-associated antibody blunting may persist longer than infancy without demonstrating impaired booster responsiveness.
• Interpret low antibody concentrations cautiously because immunologic thresholds do not directly establish clinical susceptibility, particularly for pertussis.
• Continue established maternal and childhood immunization schedules; this study does not support changing practice independently of guideline review.
• Discuss preschool booster timing as a research and policy question rather than an evidence-supported individual-care modification.
• Monitor larger studies for clinical infection outcomes, antibody persistence, and validation across different vaccine schedules and populations.