Safety of Influenza Vaccination During Pregnancy

Despite a large body of scientific evidence attesting to the safety of vaccination, many women refuse to have influenza vaccinations during pregnancy believing that the vaccine will harm their child. Their healthcare providers sometimes support this belief. The evidence strongly supports that a vaccination will lower the risk for flu in parturients, who are at increased risk for serious complications, including death, from both seasonal and novel (eg, theH1N1 pandemic) influenzas compared with an age-matched population. The vaccination also reduces the risk of infant infection. No studies to date have shown an increased risk of either maternal complications or adverse fetal outcomes associated with inactivated influenza vaccination, and no evidence exists that thimerosal-containing vaccines cause adverse events among children born to women who received flu vaccine during pregnancy. This article reviewed the evidence on which the Centers for Disease Control and Prevention (CDC) andother obstetrics-related organizations recommend routine flu vaccinations for all women who are or will be pregnant during the flu season. The CDC has placed pregnant women in the highest-priority group to receive vaccination. The authors summarized data on the safety outcomes of 11 large studies of influenza immunization during pregnancy, including a combined population of >10,000 cases (and thousands of nonvaccinated controls). None of the studies suggested any significant harmful effects in maternal morbidity or infant outcomes related to inactivated influenza during pregnancy. From April 15 to May 18, 2009, there were 34 confirmed or probable cases of H1N1 influenza in parturients reported to the CDC. Of these, 32% required hospitalization, making pregnant women greater than 4 times more likely to be hospitalized for H1N1-related complications than the general population. In addition, parturients accounted for 13%of all deaths fromH1N1 during this period, with most of themothers who died having been healthy prior to their influenza illness. Pregnant women who became ill in the flu pandemics of 1918 and 1957 also accounted for a large percentage of the morbidity and mortality from influenza. The combination of impaired cell-mediated immunity and the physiologic changes of pregnancy make parturients vulnerable to serious flu-related complications. Those with coexisting medical conditions (eg, asthma, diabetes mellitus) are at even greater risk for severe morbidity. The authors concluded that inactivated influenza vaccine can be safely and effectively administered during any trimester of pregnancy and there is no evidence suggesting that thimerosal-containing vaccines cause adverse events among children born to parturients who have been vaccinated. In fact, immunization of the mother and other family members removes several sources of viral exposure to the infant. Their findings strongly suggest that obstetrical healthcare workers should play a pivotal role in helping to protect women and newborns from this vaccine-preventable disease. It is essential that healthcare personnel encourage vaccination among parturients against both pandemic and seasonal influenza.