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

BackgroundPregnant women were identified as a population of priority for vaccination during the H1N1 influenza pandemic outbreak in 2009. ObjectivesTo assess adverse fetal outcomes following the administration of H1N1 pandemic vaccination during pregnancy. Search strategyPubMed, Embase, and Cochrane Library were searched up to January2017. Selection criteriaCohort studies investigating fetal outcomes after H1N1 influenza vaccination during pregnancy were eligible. The language was limited to English. Data collection and analysisPairs of reviewers independently screened studies for eligibility, assessed the risk of bias, and extracted data from the included studies. Main resultsA 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. ConclusionsThe 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. H1N1 vaccination during early pregnancy was not associated with an increased fetal risk; the quality of evidence was not adequate to reach a definitive conclusion.