Influenza A/H1N1 MF59 adjuvanted vaccine in pregnant women and adverse perinatal outcomes: multicentre study

Objective To assess the risk of adverse perinatal events of vaccination of pregnant women with an MF59 adjuvanted vaccine. Design Cross sectional multicentre study. Setting 49 public hospitals in major cities in Argentina, from September 2010 to May 2011. Participants 30 448 mothers (7293 vaccinated) and their 30 769 newborns. Main outcome measure Primary composite outcome of low birth weight, preterm delivery, or fetal or early neonatal death up to seven days postpartum. Results Vaccinated women had a lower risk of the primary composite outcome (7.0% (n=513) v 9.3% (n=2160); adjusted odds ratio 0.80, 95% confidence interval 0.72 to 0.89). The propensity score analysis showed similar results. Adjusted odds ratios for vaccinated women were 0.74 (0.65 to 0.83) for low birth weight, 0.79 (0.69 to 0.90) for preterm delivery, and 0.68 (0.42 to 1.06) for perinatal mortality. These findings were consistent in further subgroup analysis. No significant differences in maternal outcomes were found. Conclusion This large study using primary data collection found that MF59 adjuvanted A/H1N1 influenza vaccine did not result in an increased risk of adverse perinatal events and suggested a lower risk among vaccinated women. These findings should contribute to inform stakeholders and decision makers on the prescription of vaccination against influenza A/H1N1 in pregnant women.