A systematic review and meta‐analysis of fetal outcomes following the administration of influenza A/H1N1 vaccination during pregnancy

Abstract Background Pregnant women were identified as a population of priority for vaccination during the H1N1 influenza pandemic outbreak in 2009. Objectives To assess adverse fetal outcomes following the administration of H1N1 pandemic vaccination during pregnancy. Search strategy PubMed, Embase, and Cochrane Library were searched up to January 2017. Selection criteria Cohort studies investigating fetal outcomes after H1N1 influenza vaccination during pregnancy were eligible. The language was limited to English. Data collection and analysis Pairs of reviewers independently screened studies for eligibility, assessed the risk of bias, and extracted data from the included studies. Main results A total of 19 cohort studies were eligible. The use of vaccines during any period of pregnancy was associated with lower risk of stillbirth (adjusted hazard ratio 0.80, 95% confidence interval 0.69–0.92). No significant differences were found between the vaccinated versus unvaccinated groups in terms of the risks of spontaneous abortion, premature birth, and small for gestational age. Conclusions The administration of H1N1 vaccines during pregnancy might reduce the risk of stillbirth, a complication associated with H1N1 infection. The quality of evidence was, however, not adequate to reach a definitive conclusion.