Tdap vaccination in pregnancy effective in preventing pertussis in infants

1. Maternal vaccination with tetanus toxoid, reduced diphtheria toxoid, acellular pertussis (Tdap) during pregnancy was found to be highly effective in preventing pertussis in newborns during the first year of life. The effect was strongest in the first 2 months of life.

2. Conversely, the cocooning strategy of vaccinating postpartum women was not found to be effective in preventing pertussis in newborns.

Evidence Rating Level: 2 (Good)       

Study Rundown: Rates of pertussis infection have been increasing in recent years,. In an effort to boost protection from pertussis among the most vulnerable population, infants under 1 year old, the Centers for Disease Control and Prevention Advisory Committee on Immunization Practices (ACIP) in 2015 recommended vaccination of all pregnant women with Tdap to boost maternal antibody transfer. This study explored the effectiveness of this strategy in preventing pertussis cases among children under 1 year old, while controlling for diphtheria, tentanus and acellular pertussis (DTap) vaccination of these children. Overall, maternal vaccination during pregnancy was found to be highly protective against infant pertussis. Pertussis risk among infants of vaccinated women decreased by over 90% in the first 2 months of life. Pertussis risk continued to be low throughout the first year of life and after controlling for infant vaccination with DTap. Conversely, maternal vaccination with Tdap after pregnancy (cocooning) did not significantly decrease the risk of pertussis in infants. These findings support a standard of care that incorporates maternal Tdap vaccination as a means to protect infants from infection. While providing evidence to further support this practice, generalizability of effect is limited by the regional location of the study population.

Click to read the study, published today in Pediatrics

Relevant Reading: Effectiveness of prenatal tetanus, diphtheria, and acellular pertussis vaccination on pertussis severity in infants

In-Depth [retrospective cohort study]: Participants included infants born at Kaiser Permanente Northern California from 2010 to 2015 (N=148 981). Pertussis cases were identified through testing of clinically suspicious patients. By 2015, 87.4% of pregnant women were vaccinated during pregnancy. Of the 17 cases of pertussis identified in the first 2 months of life, only 1 was of an infant whose mother was vaccinated with Tdap in pregnancy, resulting in an unadjusted incidence rate of 0.08 (95% CI 0.00-0.43). The unadjusted incidence rate for the first year of life was 0.35 (95% CI 0.21-0.55). Pertussis risk decreased by 91.4% in the first 2 months of life and by 69% during the first year of life after adjusting for infant vaccination with DTap. Tdap vaccine effectiveness (VE) for DTap naïve infants was 87.9% (P=.009). Tdap VE was 81.4% (P=.004)for infants who had 1 DTap dose,, 6.4% (P=.901) for 2 doses and 65.9% (P=.041) for 3 doses. The percentage of mothers who received the Tdap vaccine postpartum declined from a peak of 31.7% in 2010 to a nadir of 1.8% in 2015. There was no statistically significant decrease in cases of pertussis among women who received postpartum vaccination compared to those not vaccinated at all.

Image: PD

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