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 6 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. 

A review over the 2010–2016 United States (U.S.) influenza seasons found influenza vaccination was 40% (95% confidence interval 12–59%) effective in preventing laboratory-confirmed influenza hospitalisation of pregnant women, despite a low average vaccination rate of 16% (range 8–21%). This was slightly lower than 44% (95% confidence interval 5–67%) effective in preventing symptomatic laboratory-confirmed influenza in pregnant women who did not require hospitalisation over 2010–2012 but similar to the pooled vaccine effectiveness of 41% (95% confidence interval 34–48%) in prevention of laboratory-confirmed influenza hospitalisations in adults aged 18–64 years over the 2010–2015 influenza seasons. 

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 laboratoryconfirmed 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. 

No association has been found between maternal vaccination with influenza or pertussis (Tdap) vaccines and infant hospitalisation or death within the first 6 months of life.