Impact of maternal Tdap vaccination during pregnancy on infant pertussis severity

Background:

Infants too young to receive the first dose of DTaP vaccine are at the greatest risk of severe disease and death from pertussis. All women are recommended to receive Tdap vaccine at 27-36 weeks gestation of each pregnancy to protect infants in the early weeks of life. Limited data show that this strategy reduces the risk of pertussis among infants <2 months of age however no studies have evaluated the impact on the outcomes of infected infants. We evaluated whether infants whose mothers received Tdap vaccine during pregnancy had less severe pertussis illness.

Methods:

Surveillance reports and hospital medical records for infants with pertussis at <2 months of age in California from January 2012-April 2015 were reviewed. Infants were considered exposed if their mother self-reported or had documented receipt of Tdap at any point during pregnancy and unexposed if their mother did not receive Tdap during pregnancy or received Tdap postpartum. Using chi-square tests and conditional logistic regression we estimated the impact of maternal Tdap vaccination during pregnancy on severe outcomes (hospitalization, ICU admission, intubation and death).

Results:

Of 487 reported infants, 261 (54%) had complete maternal Tdap vaccination histories.  Of these, 193 (74%) were hospitalized, 80 (42%) were admitted to an ICU, 21 (11%) required intubation and 6 (2%) died. Infants whose mothers received Tdap vaccine during pregnancy were significantly less likely to be hospitalized (OR 3.4; 95% CI 1.6-7.2), fewer were admitted to an ICU (OR 2.7; 95% CI 0.9-8.7) and none required intubation or died.  Among hospitalized infants, those whose mothers received Tdap during pregnancy had shorter hospital stays (median 3.0 vs. 6.0 days, p value 0.04).  When controlling for age in weeks, race/ethnicity, and year of onset, maternal vaccination with Tdap during pregnancy remained protective against hospitalization (OR 3.3; 95% CI: 1.4-7.8).

Conclusion:

Tdap vaccination during pregnancy protected against hospitalization in neonates with pertussis and resulted in shorter hospital stays, fewer ICU admissions, less intubation and death. More data are needed to fully assess the protective benefits of this strategy in reducing the morbidity and mortality of pertussis among infants.