Risk of Fetal Death after Pandemic Influenza Virus Infection or Vaccination- NEJM


During the 2009 H1N1 pandemic pregnant women were at risk for severe influenza. Concerns over vaccine safety in pregnant women were raised based on anecdotal reports of fetal death after vaccination. The following is a brief summary of the study published in the January 24, 2013 issue of The New England Journal of Medicine. [1]

  • 117,347 eligible pregnancies in Norway were followed looking at national registries, vaccination status, birth outcomes and background information.
  • Fetal mortality rate was 4.9 per 1000 births. 54% of pregnant women were vaccinated during that period.
  • Vaccination during pregnancy reduced the risk of influenza diagnosis. (hazard ratio 0.3)
  • Among pregnant patients with a clinical diagnosis of influenza the risk of fetal death increased (hazard ratio 1.91)
  • Risk of fetal death was reduced with vaccination during pregnancy though not significantly. (hazard ratio 0.88)


  • 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.
  • Vaccination itself was not associated with increased fetal mortality and may have reduced the risk of influenza-related fetal death during the pandemic.