Tdap in the Third Trimester: Is It Really Safe for Moms and Babies?

Giving the Tdap vaccine in the third trimester of pregnancy did not increase the risk of adverse events among mothers or infants, according to the results of a preliminary study evaluating the vaccine in pregnancy. 

Pertinent Points

- Giving the Tdap vaccine in the third trimester of pregnancy did not increase the risk of adverse events among the mothers or infants.

- The Tdap vaccine, when given during pregnancy, raised the concentrations of pertussis antibodies in infants during the first two months of life.

- More research is needed to evaluate the safety and efficacy of Tdap immunization during pregnancy.

The shot, which vaccinates against tetanus toxoid, reduced diphtheria toxoid, and acellular pertussis, also appeared to protect newborns from pertussis when given to their mothers in the third trimester, the researchers indicated. They noted that no cases of pertussis occurred. The authors reported that they found high concentrations of pertussis antibodies in infants during the first two months of life.

The small, randomized, double-blind, placebo-controlled trial was conducted from 2008 to 2012 and included 48 pregnant women. Thirty-three of the women received the Tdap vaccine, while 15 were given a placebo. The shots were administered between 30 and 32 weeks’ gestation. Women who received the placebo during pregnancy were given the Tdap vaccine postpartum prior to hospital discharge, and women who received the Tdap vaccine during pregnancy were given placebo postpartum.

There were no reported Tdap-associated serious adverse events reported in the study. Minor injection site reactions after Tdap immunization were reported in 26 of the women who received the shot during pregnancy (78.8% [95% CI, 61.1%-91.0%]) and 12 of the postpartum women (80% [95% CI, 51.9%-95.7%]), the authors reported. Most of these reactions involved pain at the injection site.

Flor M. Munoz, MD, of Baylor College of Medicine in Houston, and colleagues, conducted the trial, the results of which were published in JAMA.

In an accompanying editorial, Natalia Jimnez-Truque, MSCI, PhD, and Kathryn M. Edwards, MD, of Vanderbilt University Medical Center in Nashville, suggested that continued reporting of pertussis cases will be needed to assess the effectiveness of administering the vaccine during pregnancy. Furthermore, they raised the concern of the possibility of the prenatal vaccine interfering with the DTaP vaccine later given to infants. However, in the preliminary study, it was noted that the antibody responses in infants born to women receiving Tdap during pregnancy were not different following the fourth dose of DTaP.

“Last, future research must address the safety and immunogenicity of repeated doses of Tdap during each pregnancy, because frequent immunization might lead to a blunted antibody response," Jimnez-Truque and Edwards suggested in the editorial.