Investigating Tetanus, Diphtheria, Acellular Pertussis Vaccination During Pregnancy and Risk of Congenital Anomalies.

INTRODUCTION: This observational retrospective matched cohort study evaluated the safety of a prenatal tetanus, diphtheria, acellular pertussis (Tdap) vaccination, Boostrix. We previously reported on the risk of maternal and neonatal outcomes; here we report on the risk of congenital anomalies in infants at birth through 6 months of age. METHODS: The study included pregnant Kaiser Permanente Southern California members. Women who received the Tdap vaccine on or after the 27th week of pregnancy between January 2018 and January 2019 were matched to women who were pregnant between January 2012 and December 2014 and were not vaccinated with Tdap during pregnancy. Unadjusted and adjusted relative risks (aRRs) with 95% confidence intervals were estimated by Poisson regression. Quantitative secular trend analyses, from 2011 to 2017, were conducted on congenital anomalies with a statistically significant aRR > 1. RESULTS: The analysis consisted of 16,350 and 16,088 live-born infants in the Tdap-exposed and unexposed cohorts, respectively. Of the 14 congenital anomaly body systems evaluated, 8 (eye, ear/face/neck, respiratory, upper gastrointestinal, genital, renal, musculoskeletal, integument) had statistically significant elevated aRRs, with point estimates ranging from 1.17 to 2.02. The observed elevated aRRs were consistent with their respective secular increases over time. CONCLUSION: Cautious interpretation of these findings is warranted as these increases may have resulted from improved identification and diagnosis. Furthermore, the biological plausibility of an association between maternal vaccine exposure in the third trimester of pregnancy and birth defects is low. The overall study findings support the safety of maternal immunization with Boostrix during the third trimester of pregnancy. TRIAL REGISTRATION: ClinicalTrials.gov identifier, NCT03463577.