Safety of Tetanus, Diphtheria, Acellular Pertussis With 5 Acellular Pertussis Components (Tdap5) Vaccination During Pregnancy

Safety of Tetanus, Diphtheria, Acellular Pertussis With 5 Acellular Pertussis Components (Tdap5) Vaccination During Pregnancy: A Cohort Study Using US Electronic Medical Record Data

The purpose of this study is to evaluate the safety of Adacel vaccine among pregnant individuals exposed to Adacel at any point between the 1st day of the 27th week of gestation up to the end of pregnancy and their offspring (ie, Adacel-exposed cohort), in comparison with pregnant individuals not vaccinated with any Tdap vaccines during pregnancy and their offspring (ie, Tdap-unvaccinated comparator cohort).

The primary objectives are to estimate incidence rates and relative risks for each prespecified pregnancy outcome in Adacel-exposed and Tdap-unvaccinated comparator cohorts and for each prespecified adverse birth outcome in the offspring of both cohorts.

The secondary objectives are to estimate incidence rates and relative risks for each prespecified adverse fetal and neonatal outcome in the offspring of Adacel-exposed and Tdap unvaccinated comparator cohorts and for each prespecified adverse outcome for pregnant individuals in both cohorts.

This is a retrospective cohort study utilizing existing EHR data to identify eligible pregnant individuals, with an observation period spanning January 2016 through December 2024. Given this study design, follow-up for all pregnancies with documented deliveries is expected to be complete by December 2025.

The study report is expected to be completed by 31 December 2026.

Inclusion Criteria:

• For pregnant individuals:

  • Continuous enrollment, with no more than a 1-month administrative gap from 90 days prior to their last menstrual period (LMP)
  • Continuous enrollment for the duration of their pregnancy through delivery or termination of pregnancy (or 6 weeks postpartum for preeclampsia/eclampsia and 28 days for PPH) unless censored at death in order to capture study outcomes
  • At least 1 prenatal visit prior to 27 weeks of gestation during pregnancy

• For offspring:

  • Infants delivered by pregnant individuals who meet all the inclusion criteria above
  • With gestational age as calculated based on date of birth recorded in the EMR

Exclusion Criteria:

• For pregnant individuals:

  • Loss of pregnancy or with delivery before 27 weeks of gestation
  • Vaccinated with Boostrix® (Tdap vaccine, GSK), or with an unknown brand of Tdap vaccine, or Td (tetanus, diphtheria) vaccine during pregnancy
  • Vaccinated with any Tdap vaccine prior to the ACIP recommended optimal timeframe of ≥ 27 0/7 weeks of gestation
  • Received more than one Tdap vaccine during pregnancy
  • Vaccinated with one or more live vaccines during pregnancy
  • Pregnant individuals with multiple gestation pregnancies (eg, twins, triplets)

• For offspring:

  • Infants delivered by pregnant individuals who meet any of the exclusion criteria above