Maternal Tdap Tied to Lower Early Pertussis Immunity, but Age-4 Booster Restores Protection
A small observational cohort study found that children born to mothers who received Tdap during pregnancy had lower early antibody responses to their own DTaP vaccinations. By age 4, before a booster, pertussis and diphtheria immunity remained lower than in children of unvaccinated mothers. After the age-4 DTaP booster, antibody levels became similar and robust in both groups.
All children received DTaP at 3, 5, and 12 months. At age 3, children of Tdap-vaccinated mothers had anti-pertussis toxin IgG GMC 2.44 IU/mL versus 5.76 IU/mL in children of unvaccinated mothers; the gap persisted at age 4. Cord-blood anti-PT IgG was higher with maternal vaccination (93.7 vs 18.4 IU/mL), and anti-diphtheria seroprotection at birth was 100% vs 62%.
After the age-4 DTaP booster, anti-PT IgG GMCs were similar (247 vs 270 IU/mL). The researchers concluded pregnancy Tdap still offers important infant protection and that booster response was not impaired. The study extended the Finnish MIFI trial; 30 children of vaccinated mothers and 15 of unvaccinated mothers completed pre-booster visits at age 4.
Findings may reassure pregnant women and clinicians that maternal Tdap's early blunting does not leave children unprotected after age-4 booster. Families and pediatric practices could use this to support on-time vaccination. Public health messaging may need to explain that lower early antibody levels do not necessarily mean loss of protection, while monitoring continues. Infants