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HomeEditor's PickBooster vaccine during pregnancy cuts pertussis incidence in infants

Booster vaccine during pregnancy cuts pertussis incidence in infants

EdPickPregnancyAmong 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 two months of life – the critical period before babies can receive their first childhood acellular pertussis (DTaP) vaccination.

The findings were from the Kaiser Permanente Vaccine Study Centre (KPVSC).

Pertussis, or whooping cough, is a respiratory infection caused by the bacteria Bordetella pertussis that can affect persons of any age, but is particularly virulent and life-threatening in infants.

In addition to the protection afforded in the first two months, the study found that maternal Tdap vaccination during pregnancy reduced pertussis risk by an estimated 69% for the entire first year of life, after adjustment for the effects of infant DTaP vaccinations administered starting at age two months.

The study is the latest in a seminal and influential body of work on pertussis vaccines by the Vaccine Study Centre. KPVSC research was the first to show that the acellular pertussis DTaP vaccine, introduced in the 1990s, did not provide the long-term protection of the whole cell vaccine (DTwP) that it replaced.

Furthermore, KPVSC researchers found that the protective effect of DTaP decreases dramatically soon after the last of the five recommended shots are received around ages 4 to 6. The findings explained in large part why the US was seeing increasing outbreaks of whooping cough. Further research has shown similar waning effectiveness for the Tdap booster.

"The strategy of immunising pregnant women to boost maternal antibody transfer appears to be more effective for protecting young infants against pertussis than are attempts at 'cocooning,' in which mothers and other persons in close contact with newborns are vaccinated after the birth," said Dr Nicola P Klein, senior author and KPVSC director.

In the US, primary immunisation 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 Centres for Disease Control and Prevention's Advisory Committee on Immunisation 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 maximise antibody transfer. The ACIP recommendation largely supplanted an earlier one, in place since 2006, to administer Tdap to mothers in the immediate postpartum period.

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 the ACIP recommendations 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.

"The results of this study demonstrate that maternal Tdap administered during pregnancy provides the best protection against pertussis, which strongly supports ACIP's current recommendation to administer Tdap during each pregnancy," noted Klein.

In addition, while most prior studies evaluated maternal Tdap effectiveness in infants before DTaP vaccination, the VSC evaluated the effectiveness of Tdap during pregnancy in relation to the first three 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," said Klein. "It is reassuring that at every level of DTaP exposure, children with maternal Tdap are better protected."

Abstract
Background: Vaccination against pertussis during pregnancy is recommended to protect newborns, yet there is limited information about the effectiveness of maternal tetanus toxoid, reduced diphtheria toxoid, acellular pertussis (Tdap) vaccine before the first infant dose of diphtheria, tetanus and acellular pertussis (DTaP) vaccine and during the first year of life in infants who have received DTaP.
Methods: In a retrospective cohort study of infants born at Kaiser Permanente Northern California from 2010 to 2015, we estimated the effectiveness of maternal pertussis vaccination for protecting newborns against pertussis in the first 2 months of life and in the first year of life accounting for each infant DTaP dose.
Results: Among 148 981 newborns, the vaccine effectiveness of maternal Tdap was 91.4% (95% confidence interval [CI], 19.5 to 99.1) during the first 2 months of life and 69.0% (95% CI, 43.6 to 82.9) during the entire first year of life. The vaccine effectiveness was 87.9% (95% CI, 41.4 to 97.5) before infants had any DTaP vaccine doses, 81.4% (95% CI, 42.5 to 94.0) between doses 1 and 2, 6.4% (95% CI, −165.1 to 66.9) between doses 2 and 3, and 65.9% (95% CI, 4.5 to 87.8) after infants had 3 DTaP doses.
Conclusions: Maternal Tdap vaccination was highly protective against infant pertussis, especially in the first 2 months of life. Even after infant DTaP dosing, there was evidence of additional protection from maternal Tdap vaccination for the first year of life. This study strongly supports the United States’ current recommendation to administer Tdap during each pregnancy.

Authors
Roger Baxter, Joan Bartlett, Bruce Fireman, Edwin Lewis, Nicola P Klein

[link url="https://share.kaiserpermanente.org/article/maternal-pertussis-vaccination-reduces-risk-newborns-90-percent/"]Kaiser Permanente material[/link]
[link url="http://pediatrics.aappublications.org/content/early/2017/03/30/peds.2016-4091"]Pediatrics abstract[/link]

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