Maternal Vaccination Linked to Fewer Infant Flu Hospitalizations

Maternal influenza vaccination during pregnancy was associated with 41% vaccine effectiveness (VE) against influenza hospitalization among infants in Singapore, according to a retrospective cohort study published in JAMA Network Open. Effectiveness estimates remained statistically significant across all pregnancy trimesters and whether vaccination occurred in the current or prior influenza season.

The study included 221,185 infants who were Singapore citizens or permanent residents, born from May 1, 2017, through December 1, 2023, had complete maternal and infant sociodemographic data, and survived at least 2 weeks after birth. Maternal vaccination status from the National Immunization Registry was linked to infant outcomes through the national birth registry. The primary outcome was influenza hospitalization from birth to age 6 months, identified in national health care claims. Overall, 25.9% of infants were born to vaccinated mothers.

Infants born to vaccinated mothers had a lower adjusted hazard of influenza hospitalization than infants born to unvaccinated mothers (adjusted hazard ratio, 0.59; 95% CI, 0.45-0.77). Estimated VE against hospitalization was 41% (95% CI, 23%-55%).

Estimated VE was 52% (95% CI, 20%-71%) for first-trimester vaccination, 37% (95% CI, 12%-56%) for second-trimester vaccination, and 41% (95% CI, 8%-64%) for third-trimester vaccination. VE was 41% when vaccination occurred in the current influenza season (95% CI, 12%-61%) and 41% after vaccination in the prior season (95% CI, 19%-58%).

The authors noted that reliance on diagnostic codes may have underestimated severe influenza because the illness can present nonspecifically in infancy. They also acknowledged potential unmeasured confounding, although negative outcome controls showed no suggestion of residual confounding. Influenza subtype–specific VE could not be assessed, and the findings may not generalize to other populations, particularly those of non-Asian ethnicity. The authors concluded that vaccination at any point in pregnancy could potentially simplify rollout in regions with year-round influenza transmission while protecting infants against severe influenza.

Source: Wee LE, Goh NS, Ho RWL, et al. Vertical vaccination against infant influenza hospitalization in a tropical setting. JAMA Netw Open. 2026;9(8):e2628389. doi:10.1001/jamanetworkopen.2026.28389