It's shocking to me that we still see pertussis deaths in children in the United States. While the factors contributing to the current picture are complex, it is becoming very clear how we can prevent such deaths in the future.
Source: Baxter R, Bartlett J, Fireman B, et al. Effectiveness of vaccination during pregnancy to prevent infant pertussis. Pediatrics. 2017;139(5):e20164091: doi:10.1542/peds.2016-4091. See AAP Grand Rounds commentary by Dr. Rebecca Brady (subscription required).
This is a great study from Kaiser Permanente of Northern California, an organization long recognized for high-quality studies of immunization. The current study, involving almost 150,000 infants born between 2010 and 2015, strongly suggests that immunizing pregnant women with the adult tetanus-diphtheria-acellular pertussis vaccine (recommended at 27-36 weeks gestation) greatly decreased pertussis risk in newborns, both in the first 2 months of life and in the first year of life. The numbers showed 1 case of pertussis under 2 months of age in an infant born to an immunized mom, and 16 cases in infants born to unimmunized moms, for a vaccine efficacy of 91%. The strategy also was effective up to a year of age, the longest period these infants were assessed for this study. However, maternal immunization after delivery (the cocooning approach) or prior to pregnancy did not seem to be effective in preventing pertussis in these infants. Thankfully, none of the children with pertussis in this study died, although several required hospitalization. Let me highlight some nice features of this study.
The timing of the study was well-suited to assess effects of maternal pertussis immunization because national guidelines were evolving over this time. In 2006, the Advisory Council for Immunization Practices (ACIP) recommended immunization of pregnant women only in the postpartum period, a form of "cocooning" to hopefully shield young infants from being exposed to pertussis illness in their mothers while they were still too young to have benefited from their own immunizations starting at 2 months of age. In 2011, ACIP recommended prepartum immunization during pregnancy for mothers who had not received pertussis vaccination, and then in 2013, this was updated to include all pregnant women for every pregnancy, regardless of prior immunization history. Thus, this Kaiser study had a mix of women who were covered by these evolving recommendations, allowing for better differentiation of best strategies.
Another jewel in this study is that the authors used some clever statistics and logic to determine whether maternal prepartum immunization might actually interfere with the immune response of their infants when they themselves received pertussis immunizations. This was a theoretical risk, since the presence of maternal pertussis antibody in the infant's system could block infant immune response, and in fact, this was seen in the era of the whole cell pertussis vaccine. The Kaiser study did not detect any evidence of interference by maternal antibody.
Overall this was a very well-planned and reported study providing us with valuable data to recommend universal pertussis immunization for pregnant women.
