Vaccine for H1N1 helped prevent fetal deaths

A study published online by The New England Journal of Medicine has determined that vaccination for H1N1 influenza during the pandemic of 2009 did not result in an increase in fetal mortality. The researchers performed an analysis of data on 113,331 women in Norway who became pregnant 43 weeks before December 31, 2010. They used the national health registries and data regarding reimbursement of primary care physicians in Norway to assess the effectiveness of the pandemic vaccine in pregnant women and the effect of vaccination or influenza on fetal survival.

Before 2009, pregnant women in Norway were not routinely advised to be vaccinated against seasonal influenza. During the pandemic, a trivalent seasonal influenza vaccine and an H1N1 vaccine with an AS03 adjuvant were recommended for high-risk groups, although it was recommended that pregnant women receive the pandemic vaccine only, in the second or third trimester, according to the study.

Pandemic influenza vaccinations were offered starting October 19, 2009, and nearly all (97%) were administered by December 31, 2009. A total of 25,976 children were born after their mothers were vaccinated during pregnancy, with almost all vaccinations occurring during the second or third trimester. Among the vaccinated women, there were 78 fetal deaths, compared with 414 in the 87,335 women who were pregnant during the pandemic who were unvaccinated. The researchers also considered nonfatal birth outcomes (preterm delivery and low birth weight and Apgar score at term) and found no evidence of an association between vaccination and these outcomes.

The researchers concluded that pandemic influenza virus infection in pregnancy was associated with an increased risk of fetal death. Vaccination during pregnancy reduced the risk of an influenza diagnosis. It was not, however, associated with increased fetal mortality, and may have reduced the risk of influenza-related fetal death during the pandemic.