Effectiveness and safety of inactivated influenza vaccines during pregnancy

How effective is the inactivated influenza vaccine when given during pregnancy?

The immune response to influenza vaccination in pregnant women is similar to that of non-pregnant women. The efficacy (prevention of illness among vaccinated individuals in controlled trials) and effectiveness (prevention of illness in vaccinated populations) of influenza vaccines is dependent on several factors. The age and immune status of the recipient are important as well as the match between circulating viral strains and the vaccine.

Influenza vaccination during pregnancy provides “two for one” protection, reducing the maternal risk of influenza disease and associated complications and the risk for their baby during the first six months after birth.

A review of acute respiratory illness (ARI) and influenza vaccination during pregnancy over the 2012 and 2013 Australian influenza seasons identified that women who received an influenza vaccination during their pregnancy were 81% less likely to attend an emergency department with an ARI, and 65% less likely to be hospitalised than pregnant women who were not vaccinated.

An increase in circulating maternal influenza antibodies after vaccination supports maximum transplacental antibody transfer to the growing baby and protection against influenza after birth. Babies born during an influenza season in 2002–2005 in the U.S. were followed until they were aged 6 months. Those born to mothers who received an influenza vaccination during pregnancy were 41% less likely to have laboratory-confirmed influenza and 39% less likely to be admitted to hospital with an influenza-like illness than babies whose mother didn’t have an influenza vaccination.

How safe is receiving the influenza vaccine during pregnancy?

Inactivated influenza vaccines have been recommended for and used in pregnant women since the 1960s, along with ongoing safety monitoring and research. Influenza vaccination during pregnancy has an excellent safety record for the woman herself, the growing baby and newborn.

Studies comparing hundreds of thousands of vaccinated women with unvaccinated women have identified a lower incidence of stillbirth for vaccinated women and no difference in the incidence of preterm births, or occurrence of congenital malformations. No relationship between maternal influenza vaccination and spontaneous abortion has been identified.