Pregnant women are about seven times more likely to be hospitalized or die from influenza virus infections than women of the same age who are not pregnant. For that reason, pregnant women are recommended to receive an influenza vaccine early in pregnancy.
Recently, a group of researchers at the University of Adelaide in Australia did a retrospective analysis of 19 observational studies to determine whether the influenza vaccine was safe when given during pregnancy (M. McMillan K, Porritt K, Kralik D, et al. Influenza Vaccination During Pregnancy: A Systematic Review of Fetal Death, Spontaneous Abortion, and Congenital Malformation Safety Outcomes. Vaccine. 2015 Apr 27;33:(18)2108-2117). Fourteen of those studies focused on the novel California H1N1/2009 strain.
The authors of the study found that the observed risk for fetal death, spontaneous abortion, and congenital malformation crossed the null value in each case. This retrospective analysis of tens of thousands of pregnant women confirms the safety of influenza for the unborn child when given during pregnancy.