Study confirms benefit of maternal Tdap vaccination in pregnancy

A new study confirms what public health officials had hoped-that maternal vaccination against pertussis can help protect vulnerable newborns.

The study, published in the American Journal of Preventive Medicine, reviewed thousands of records to test the theory that maternal vaccination would offer immunity to infants too young to be vaccinated themselves.¹

“Pediatricians should share the message that pregnant mothers should receive the Tdap vaccine in pregnancy to reduce infant pertussis,” says lead study author Sylvia Becker-Dreps, MD, MPH, associate professor in the Department of Family Medicine, associate director of the Office of International Activities, and director of the UNC Program in Nicaragua at the University of North Carolina (UNC) at Chapel Hill. “Infants under 6 months of age whose mothers received prenatal Tdap had a 75% lower rate of pertussis hospitalizations as compared to infants of unvaccinated mothers,” she says.

Becker-Dreps and her team reviewed records from more than 675,000 pregnancies in the United States to assess whether a mother receiving the Tdap vaccine in pregnancy would be effective in reducing the chances of her infant developing pertussis in the first 18 months of life. Overall, the results of the study show that maternal vaccination with the Tdap vaccine during pregnancy showed an overall decrease in both pertussis cases and hospitalizations for pertussis in infants of the vaccinated mothers.

Pertussis, a severe respiratory infection that is particularly dangerous for infants, is on the rise, but the Centers for Disease Control and Prevention (CDC) does not recommend vaccination for infants until they are aged 2 months. In an effort to provide protection to susceptible newborns, the CDC in 2013 began recommending that mothers receive the vaccine during pregnancy in order to pass immunity on to their newborn infants. The recommendation was based on the idea that antibodies could be passed through the placenta, but there were no studies to confirm the theory.

Now, researchers are able to observe data collected in the years since the recommendation. The research team observed a 75% reduction in the number of pertussis hospitalizations, and a 46% reduction in overall pertussis cases in infants aged younger than 6 months whose mothers had received the Tdap vaccination during pregnancy.

“The clinical outcomes show that the immunity passed from mother to fetus during pregnancy protected the infant during the first 6 months of life, before the infant completes the full course of the pertussis vaccine [itself],” researchers note.

The study also showed that maternal vaccination did not-as some thought it might-reduce the infant’s response to its own Tdap vaccine series.

“This just adds more fuel to the fire for encouraging women to get Tdap during pregnancy,” Becker-Dreps says. “A lot of women are concerned about vaccines in general, but you really might be harming your baby by not getting this vaccine.”

The study also examined optimal timing for the vaccine during pregnancy and found that the third trimester, but at least 2 weeks before delivery, appears to offer the best protection. No vaccination benefits were observed in this study for mothers who received the vaccine before the third trimester, the report notes.

The CDC currently recommends that pregnant mothers receive the Tdap vaccine at between 27 and 36 weeks of pregnancy.

References:

1. Becker-Dreps S, Butler AM, McGrath LJ, et al. Effectiveness of prenatal tetanus, diphtheria, acellular pertussis vaccination in the prevention of infant pertussis in the U.S. Am J Prev Med. 2018;55(2):159-166.