Flu vaccine during pregnancy cuts infant infection risk by 41%

Vaccinating pregnant women against seasonal influenza reduced the risk of laboratory-confirmed influenza, cuts infection in their infants by 41 percent a study finds.

Maternal immunization similarly cut by 39 percent the risk that infant up to 6 months of age would be hospitalized for influenza-like illness.

Influenza vaccination is already recommended for pregnant women to reduce their risk of developing flu-related complications. “These findings provide support for the added benefit of protecting infants from influenza virus infection up to 6 months, period when infants are not eligible for influenza vaccination but are at the highest risk of severe influenza illness.”

Even though such immunization is recommended during pregnancy, it is not well accepted in the United States and many pregnant women do not get vaccinated. Since it would be unethical to perform a randomized, controlled study of maternal vaccination, a nonrandomized observational study to assess whether immunization during pregnancy conferred protection to infants was conducted.

The study subjects were 1,160 mother-infant pairs in which approximately half the mothers (573) had chosen to receive seasonal flu vaccine while pregnant and other half (587) had declined the vaccine. All were enrolled after delivering healthy singleton infants at 7 hospitals serving the Navajo and White Mountain Apache Indian reservations in the southwestern United States during three flu seasons between 2002 and 2005.

A total of 605 infants developed influenza-like illness during the flu season following delivery.

“Found a 41 percent reduction in the risk of laboratory-confirmed influenza virus infection for infants of influenza-vaccinated mothers compared with infants of unvaccinated mothers.”

The incidence of influenza-like illness was 6.7 per 1,000 person-days for infants of mothers who had not.

Among the infants whose mothers were vaccinated, there was a 41 percent reduction in the risk of laboratory-confirmed influenza virus infection compared with those mothers who declined vaccination.

When the analysis was restricted only to cases of influenza that required hospitalization, a 39 percent reduction in risk was found for infants of women who had been vaccinated, compared with those of mothers who had not been vaccinated.