Effectiveness of prenatal tetanus, diphtheria, and acellular pertussis vaccination on pertussis severity in infants

Background. All US women are recommended to receive a tetanus, diphtheria, and acellular pertussis (Tdap) vaccine at 27-36 weeks gestation during each pregnancy to reduce the risk of pertussis to their infants. The impact of this strategy on severity of disease among infected infants has not been evaluated. Methods. We use a retrospective cohort study design evaluating whether pertussis-infected infants born in 2011-2015 whose mothers received Tdap vaccine during pregnancy had less severe pertussis, resulting in a lower risk of hospitalization or intensive care unit admission compared with infants born to unvaccinated mothers. Results. Infected infants of vaccinated mothers were significantly less likely to be hospitalized and had significantly shorter hospital stays compared with infants born to unvaccinated mothers, after adjustment for chronological and gestational age and receipt of diphtheria and tetanus toxoids and acellular pertussis vaccine. Unadjusted and adjusted vaccine effectiveness for preventing hospitalization among infants with pertussis was 72% (95% confidence interval [CI], 49%-85%) and 58% (95% CI 15%-80%), respectively. No infants born to vaccinated mothers required intubation or died of pertussis. Conclusions. Infants with pertussis whose mothers received Tdap during pregnancy had a significantly lower risk of hospitalization and intensive care unit admission and shorter hospital stays. Prenatal Tdap vaccination is a critical strategy for reducing the morbidity and mortality from pertussis.