Infants whose mothers received prenatal Tdap were more than 40% less likely to experience pertussis when compared with infants of mothers who were not immunized, according to recently published research in the American Journal of Preventive Medicine.
“This just adds more fuel to the fire for encouraging women to get Tdap during pregnancy,” Sylvia Becker-Dreps, MD, MPH, associate professor in the department of family medicine at the University of North Carolina School of Medicine and the department of epidemiology at the UNC Gillings School of Global Public Health, said in a press release. “A lot of women are concerned about vaccines in general, but you really might be harming your baby by not getting this vaccine.”
To determine the clinical effectiveness of prenatal Tdap in preventing infant pertussis and how it varies by gestational age at administration, the researchers conducted a nationwide cohort study of pregnant women and infants delivered between June 2010 and December 2014. The researchers analyzed insurance claims to ascertain if women received prenatal Tdap vaccination and whether infants up to the age of 18 months were hospitalized or made outpatients visits for pertussis.
The researchers studied 675,167 mother-newborn pairs. There were 90,445 women (13.4%) who received prenatal Tdap during pregnancy at least 2 weeks before delivery, 5,872 women (0.9%) who were vaccinated during 2 weeks before delivery and 36,470 women (5.4%) who received the vaccine on the day they delivered their infant or within 7 days following delivery.
There was a 43% lower rate of pertussis and a 68% lower rate of inpatient-only pertussis among the infants whose mothers received prenatal Tdap compared with infants whose mothers did not receive prenatal or postpartum Tdap (HR = 0.57; 95% CI, 0.35-0.92; HR = 0.32; 95% CI, 0.11-0.91).
The timing of the immunization was significant, because women who received prenatal Tdap at 27 weeks’ gestation or later had infants who experienced lower rates of pertussis compared with the infants of unimmunized mothers (HR = 0.42; 95% CI, 0.23-0.78). There was no reduction in pertussis rates for children whose mothers received Tdap before 27 weeks’ gestation (HR = 1.10; 95% CI, 0.54-2.25).
“Prenatal Tdap provided a substantial reduction in infant pertussis during the period of life with the highest pertussis burden,” the researchers concluded. “Increasing use of Tdap in pregnancy would be anticipated to reverse the current trends of pertussis incidence among infants in the U.S.”
“Our results showed that getting the vaccine during the third trimester, but at least two weeks before delivery, is best to optimize the benefits of the vaccine,” Becker-Dreps said.
The researchers added that the study results reinforce the CDC recommendation that women should get a Tdap booster during each pregnancy to provide immunity to children, with optimal timing of administration at 27 to 36 weeks’ gestation. – by Bruce Thiel
Disclosure: Becker-Dreps reports receiving investigator-initiated research funds from Pfizer for a study on pneumococcal vaccines and serving as a vaccine consultant for Pfizer.