Since September 2014, reduced antigen diphtheria-tetanus-acellular pertussis (Tdap) vaccine has been included in Brazil’s maternal immunization program. Researchers looked at the links between maternal Tdap vaccination and pregnancy-related and newborn AEs of interest. The data from medical charts of 1203 pregnant women who received Tdap as part of the maternal immunization program and delivered between May 2015 and February 2017 and 1259 unvaccinated women who delivered between September 2012 and August 2014 were compared in this descriptive, observational, retrospective, single-center study in Brazil. The moment of immunization or 27 gestational weeks were used as index dates. Cumulative occurrences were determined by dividing the number of women who experienced each incident between the index and delivery dates by the total number of women in the exposed cohort who had a vaccination date available or the total number of women in the unexposed cohort. In the exposed versus unexposed cohorts, the cumulative incidences per 1000 people were 8.34 versus 17.47 for gestational diabetes, 9.17 versus 24.62 for pregnancy-related hypertension, 3.34 versus 15.09 for pregnancy hemorrhage, 53.38 versus 96.11 for preterm birth, and 57.55 versus 49.25 for small for gestational age. 

Following maternal Tdap vaccination, there was no elevated risk of pregnancy-related AEs or newborn AEs of interest.Due to the extreme limitations of retrospective observational studies, these findings should be taken with caution.