Flu shots in pregnant mums lower infant infection rates

Maternal influenza vaccination during pregnancy appears to reduce the incidence of infection in infants, with the protective effect being more pronounced when vaccination is administered in the second or third trimester, according to a study.

The study involved pregnant individuals enrolled in Kaiser Permanente Northern California (KPNC) and their infants. The researchers followed the infants from birth to the first occurrence of a positive polymerase chain reaction test result for influenza, age 6 months, death, disenrollment from KPNC, or the end of the study.

Researchers examined the association between vaccination and infant influenza outcomes any time during pregnancy and by trimester of vaccination.

The analysis included 245,498 infants, of which 46.0 percent were born to mothers who had received flu vaccine during pregnancy. Influenza infection occurred less frequently among infants born to vaccinated mothers than among those born to unvaccinated mothers (0.12 percent vs 0.30 percent).

In multivariable Cox regression models, vaccination during pregnancy was associated with a 44-percent (95 percent confidence interval, 31.4–54.9) decrease in infant influenza infection in any clinical setting.

When assessed by trimester of vaccination, infant influenza decreased by 11.3 percent when flu vaccination occurred during the first trimester. Greater reductions of 51.5 percent and 59.3 percent were observed when vaccination occurred during the second and third trimester, respectively. Vaccine effectiveness in the second and third trimesters were significantly greater than that in the first trimester (p=0.02 and p<0.001, respectively).