Maternal Vaccination Dramatically Reduces Pertussis Risk in Newborns

Among infants of women who received the Tdap pertussis booster vaccine during pregnancy, the risk of contracting pertussis was reduced by an estimated 91% during the first 2 months of life — the critical period before they can receive their first childhood acellular pertussis (or DTaP) vaccination, according to a study published in Pediatrics.

The study population consisted of 148,981 infants born in Kaiser Permanente hospitals in Northern California from 2006-2015. The percentage of infants whose mothers received Tdap during pregnancy increased from less than 1% in 2006-2008, to nearly 12% in 2010, and over 87% by 2015, following recommendations from the Advisory Committee on Immunization Practices (ACIP) and reminders in the electronic medical record. The majority of pregnant women vaccinated in Kaiser Permanente Northern California from 2010-2015 received Tdap at 20 weeks gestation or greater; by 2013, most were vaccinated between 27-36 weeks gestation.

In addition, while most prior studies evaluated maternal Tdap effectiveness in infants before DTaP vaccination, Kaiser's Vaccine Study Center evaluated the effectiveness of Tdap during pregnancy in relation to the first 3 infant doses of DTaP to address concerns that maternal Tdap and infant DTaP may interfere with each other, potentially leading to decreased protection for the infant.

“Maternal Tdap administered during pregnancy was highly effective at protecting infants against pertussis prior to their first dose of DTaP. Through the first year of life, maternal Tdap continued to provide protection without interfering with DTaP,” Nicola P. Klein, MD, PhD, who was the paper's senior author, said in a press release about the study. “It is reassuring that at every level of DTaP exposure, children with maternal Tdap are better protected.”

In the United States, primary immunization of infants with DTaP (reduced diphtheria toxoid, tetanus toxoid, acellular pertussis) vaccines is recommended at 2, 4 and 6 months of age. In the early months of life, before newborns can benefit from DTaP, they receive some protection against pertussis from maternal antibodies transferred during pregnancy. However, without pertussis vaccination during pregnancy, maternal pertussis antibodies in the infant decline substantially by 6 weeks of age, and become undetectable by about 4 months of age.

In February 2013, the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices recommended Tdap vaccination in pregnant women regardless of prior Tdap vaccination, at any time during pregnancy, but preferably between 27 and 36 weeks gestation to maximize antibody transfer. The ACIP recommendation largely supplanted an earlier one, in place since 2006, to administer Tdap to mothers in the immediate postpartum period.

Reference

• Baxter R, Bartlett J. Fireman B, Lewis E, Klein NP. Effectiveness of Vaccination During Pregnancy to Prevent Infant Pertussis. Pediatrics. 2017; e20164091.