Review on the effects of influenza vaccination during pregnancy on preterm births.

Pregnant women are considered to be susceptible to severe influenza illness and are recommended as a priority group to be targeted for influenza vaccination in countries with vaccination programs. Increased rates of poor birth outcomes have also been temporally associated with influenza infection, especially when pandemics strains emerge. Even though the primary purpose for influenza vaccination during pregnancy is to decrease the risk of influenza infection in the women, other potential benefits include protection of their young infants against influenza illness and possibly improving birth outcomes. The 2009 influenza A/H1N1 pandemic highlighted the importance of influenza vaccination during pregnancy, after pregnant women were identified as a group with heightened morbidity and mortality during the pandemic. A few studies conducted before the 2009/10 season and a large number of reports during and after the 2009 pandemic have assessed the association between maternal influenza vaccination and birth outcomes. Although these studies indicate that influenza vaccination is safe for both the mother and the fetus, there are conflicting data on the effect of vaccination in improving preterm birth rates. We reviewed the 2 published randomized control trials and other observational studies that explored the relationship between maternal influenza vaccination and preterm births.