Flu shot during pregnancy extends protection to offspring

Influenza vaccination in pregnant women, especially during the second or third trimester, cuts the risk of infection in infants, as shown in a study.

Researchers looked at pregnant individuals enrolled in Kaiser Permanente Northern California (KPNC) and their infants to assess the effectiveness of maternal influenza vaccination during pregnancy against infection in infants during their first 6 months of life. All infants were followed from birth until the first occurrence of a positive test result for influenza, age 6 months, death, disenrollment from KPNC, or the end of the study.

The analysis included 245,498 infants, of whom 46.0 percent were born to mothers who received influenza vaccination during pregnancy.

Compared with infants born to unvaccinated mothers, those who were born to vaccinated mothers were less likely to contract influenza infection within the first 6 months of life (0.12 percent vs 0.30 percent).

Multivariable Cox regression analysis showed that vaccination during pregnancy was associated with a 44.4-percent reduced risk (95 percent confidence interval, 31.4–54.9) of influenza infection in infants in any clinical setting.

In an analysis stratified by the trimester of pregnancy the vaccination was administered, the reduction in the risk of infant influenza infection was significantly greater when mothers received their shot in the second or third trimester than in the first trimester (–51.5 percent and –59.3 percent vs –11.3 percent; p=0.02 and p<0.001, respectively).