When the CDC’s Advisory Committee on Immunization Practices (ACIP) recommended that all pregnant women receive a Tdap vaccine during each pregnancy, between 27- and 36 weeks of gestation, in October of 2012, they acknowledged that a theoretical risk exists for severe local reactions
in pregnant women vaccinated more frequently due to multiple pregnancies spaced closely together. ACIP, however, also acknowledged that no studies had ever examined the safety of administering Tdap vaccine to pregnant women during subsequent pregnancies, but reported that going forward, they planned to monitor both the Vaccine Adverse Events Reporting System (VAERS) and the Vaccine Safety Datalink (VSD) to assess for adverse events, maternal adverse pregnancy outcomes and birth outcomes.
In 2018, ACIP reported that studies on the use of Tdap vaccine in pregnancy have not shown any “new or unexpected safety concerns” but admitted that safety studies on Tdap vaccine administration during pregnancy at close intervals to another tetanus toxoid containing vaccine were limited.
In October 2022, the FDA approved the Boostrix Tdap vaccine for use in pregnant women, to be administered during the third trimester, for the prevention of pertussis in infants younger than two months of age. This approval was made based on a re-evaluation of the Boostrix data from an observational case-control study of the pertussis component of the Tdap vaccine.
The evaluation of Boostrix Tdap vaccine’s safety data in pregnant women was based on a study of 680 women, with 340 receiving a non-U.S. formulated BOOSTRIX Tdap vaccine, and 340 receiving a normal saline placebo. The FDA considered the non-U.S. formulated Boostrix Tdap vaccine to be comparable to the U.S. licensed vaccine even though the non-U.S. formulation contains less aluminum per dose. Following childbirth, the women who received a saline placebo during pregnancy were given a dose of the non-U.S. formulated BOOSTRIX Tdap vaccine. According to the FDA, the side effects of giving the vaccine to women during pregnancy were similar to women who got the vaccine after pregnancy. Additionally, the FDA reported that this study did not demonstrate any vaccine-related adverse events on the pregnancy, developing infant, or newborn infant.
In January 2023, Adacel Tdap vaccine received FDA approval for use in pregnant women, for the prevention of pertussis in infants under two months of age, to be administered during the third trimester of pregnancy. Safety of the use of Adacel vaccine in pregnant women was based on the use of vaccine in 225 women who received the vaccine during pregnancy when compared with 675 women who did not. According to data submitted to the FDA, there were three serious adverse events (SAEs) that resulted in death among the study participants. One death occurred in a fetus whose mother received Adacel Tdap vaccine at 2.5 weeks gestation. At 23 weeks gestation, the fetus was noted to have a complete atrioventricular canal defect and death occurred at 33 weeks. Details of the two additional fetal deaths were not provided, except that both reportedly occurred in women who were vaccinated more than 30 days prior to the onset of pregnancy and deemed unrelated to vaccination.
