Safety of MF59-adjuvanted A/H1N1 influenza vaccine in pregnancy: a comparative cohort study.

OBJECTIVE The 2009-2010 A/H1N1 pandemic provided a unique setting to study the safety of MF59-adjuvanted vaccination in pregnancy. STUDY DESIGN This was an observational cohort study of the safety of an MF59-adjuvanted A/H1N1 vaccine (Focetria) conducted among 4508 pregnant women (2295 vaccinated vs 2213 unvaccinated), with 3 month follow-up of neonates. RESULTS No maternal deaths or abortions occurred among the vaccinated women. No differences between the vaccinated and unvaccinated cohorts were observed for gestational diabetes, preeclampsia, stillbirth, low birthweight, neonatal deaths, or congenital malformations. The risk of premature birth was significantly decreased among the vaccinated women (adjusted proportional hazard, 0.69; 95% confidence interval, 0.51-0.92). No differences were observed in rates of congenital malformations after vaccination in the first (2.1%), second (2.7%), or third (2.1%) trimesters. CONCLUSION There was no evidence of a safety risk for MF59-adjuvanted A/H1N1 vaccination in pregnant women; protection was observed against premature birth.