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Prenatal Tdap vaccination more effective than postpartum immunization
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Tdap vaccination from 27 to 36 weeks’ gestation was 85% more effective than postpartum vaccination at preventing pertussis in infants aged younger than 8 weeks, according to a retrospective cohort study using data from the California Immunization Registry.
“This is an important study demonstrating that prenatal Tdap vaccination more effectively prevents pertussis in young infants than postpartum Tdap vaccination,” Kathleen Winter, PhD, MPH, assistant professor in the department of epidemiology at the University of Kentucky College of Public Health, and colleagues wrote. “Importantly, our study also found that vaccination during the recommended window of 27 to 36 weeks’ gestation was more protective than vaccinations received earlier in pregnancy.”
Infants aged younger than 8 weeks are at the greatest risk for death from pertussis and rely on passively acquired maternal antibodies for protection. Women are recommended to receive Tdap vaccine at the start of the third trimester of pregnancy to optimize transplacental transfer of antibodies, but no studies have previously evaluated the effectiveness of this strategy in reducing pertussis incidence in early infancy.
Winter and colleagues evaluated data from the California Immunization Registry to identify a cohort of 74,504 women who gave birth during 2013 or 2014 in California and received a recorded Tdap vaccine dose during pregnancy or within 14 days after delivery. Of these women, 58% were vaccinated during pregnancy, and 42% were vaccinated postpartum.
The corresponding infants from this cohort were matched to records from the California Department of Public Health that identify reported cases of pertussis among infants aged 12 months or younger.
According to the researchers, 119 infants were reported with pertussis and aged younger than 1 year, with an incidence of 1.6 cases per 1,000 births. Of these, 21% were aged younger than 8 weeks.
After adjusting for a number of maternal and infant covariates, the researchers found that prenatal Tdap vaccination was significantly more effective at preventing pertussis in infants aged younger than 8 weeks than postpartum vaccination.
When administered from 27 to 36 weeks’ gestation, the Tdap vaccine was 85% more effective (95% CI, 33-98) in preventing pertussis in infants aged younger than 8 weeks and 72% more effective (95% CI, 30-89) in preventing pertussis in infants aged younger than 12 weeks compared with postpartum Tdap.
Furthermore, the researchers found that infants whose mothers were vaccinated in the second trimester were significantly more like to have pertussis before 8 weeks (OR = 8.1; 95% CI, 1.3-49) and 12 weeks (OR = 4.6; 95% CI, 1.39-15.25). Data also suggested the possibility of greater vaccine effectiveness from 27 to 31 weeks’ gestation than later in the third trimester, but further research is needed to confirm and build upon those findings.
Winter and colleagues noted that, while vaccination during pregnancy may be a marker of access to and quality of prenatal care, “when placed in the multivariate model, these factors showed no association with risk of pertussis, except for that of prior births.”
“Vaccination timing is critical to maximize antibody transfer to the infant,” they wrote. “Efforts should be made by prenatal care providers to provide Tdap to pregnant women on-site during routine prenatal visits at the earliest opportunity between 27-36 weeks’ gestation.” – by Sarah Kennedy
Disclosure: The researchers report no relevant financial disclosures.
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