Infants born to mothers who received the flu vaccine during pregnancy experienced a substantial 39% lower risk of flu-related hospitalization compared to those born to unvaccinated mothers, according to a study published in JAMA Pediatrics.
Conducted by the New Vaccine Surveillance Network Collaborators, the test-negative case-control study analyzed data from 3,764 infants under 6 months old across seven pediatric care centers in seven states during flu seasons from 2016-17 to 2019-20.
The study emphasized the potential severity of maternal flu during pregnancy, linking it to adverse birth outcomes such as preterm birth, small-for-gestational-age fetuses, and miscarriage. Since infants cannot receive the flu vaccine until 6 months of age, the study focused on the impact of maternal vaccination on their vulnerability.
The researchers highlighted the efficiency of maternal immune responses to the influenza vaccine, underscoring the transfer of protective antibodies from mother to fetus.
Among the infants studied, 53% were born to mothers who received the flu vaccine during pregnancy. The overall vaccine effectiveness (VE) against flu-related emergency department visits or hospitalizations in infants was 34%. Specifically, maternal flu vaccination demonstrated 19% effectiveness against infant ED visits, 39% against hospitalization, 25% against influenza A, and 47% against influenza B in infants. VE against H1N1 and H3N2 strains was 39% and 16%, respectively.
The study revealed higher protection levels in the youngest infants, with a VE of 53% among those younger than 3 months. Additionally, VE was 52% when mothers were vaccinated in the third trimester, compared to 17% in the first or second trimester.
Despite the proven benefits, the study highlighted low global maternal influenza vaccine uptake, emphasizing the need for increased efforts to raise awareness and improve vaccination coverage during pregnancy.
In a related commentary, experts from the Wake Forest School of Medicine stressed the importance of expanding vaccine registries to cover people of all ages and promoting collaboration between obstetric and pediatric clinicians to enhance vaccine access, confidence, and coverage for maternal and infant health. The authors advocated for universal vaccine registries and collaborative efforts to optimize health outcomes for both mothers and infants.
