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Vaccination against H1N1 looks safer than influenza during pregnancy

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f375 (Published 23 January 2013) Cite this as: BMJ 2013;346:f375

Just over half the women in Norway who were in late pregnancy at the height of the influenza pandemic in 2009 received an adjuvanted vaccine against influenza H1N1. Vaccinated women were no more likely to have a fetal death than comparable unvaccinated women in a study linking five national registers (78/25 976 v 414/87 335; adjusted hazard ratio 0.88, 95% CI 0.66 to 1.17). Being pregnant during the pandemic (1.26, 1.02 to 1.55) and having flu while pregnant (1.91, 1.07 to 3.41) were both associated with an increased risk of fetal death in a series of analyses adjusted for smoking, comorbidities, body mass index, and other potential confounding factors.

The authors had data on more than 117 000 singleton pregnancies in 2009 and 2010. Pregnant women were offered vaccination during the second or third trimester, and vaccinations peaked during the intense pandemic period at the end of 2009. Most of those vaccinated had one dose of Pandemrix, which contains the adjuvant AS03. It cut their risk of having clinical influenza by 70% (0.3, 0.25 to 0.34).

Vaccination during the second or third trimester of pregnancy looks safe for the fetus, say the authors, unlike having flu during pregnancy. The study was designed, conducted, analysed, and funded independently of vaccine manufacturers.

Notes

Cite this as: BMJ 2013;346:f375