Infectious Disease
Effectiveness of maternal influenza vaccination against influenza-associated emergency department and urgent care encounters among infants aged >6 months – VISION Network, 2023–2024 and 2024–2025 seasons Emily Reeves* Emily Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Reeves Centers for Disease Control and Prevention (CDC)
Studies have shown that maternal influenza vaccination during pregnancy provides protection for infants aged <6 months, a population at increased risk of severe influenza and without a licensed influenza vaccine. We evaluated maternal influenza vaccine effectiveness (VE) against influenza-associated emergency department or urgent care (ED/UC) encounters among infants during two U.S. influenza seasons (2023-2025).
A test-negative, case-control study was conducted among infants <6 months with linkage to maternal vaccination records. Infants with acute respiratory illness (ARI)-associated ED/UC encounters who tested positive or negative for influenza and negative for SARS-CoV-2 and RSV via molecular testing at seven VISION Network health systems were included. VE was estimated using logistic regression comparing the odds of maternal influenza vaccination (≥14 days before delivery) in influenza positive cases vs influenza negative controls, adjusting for site, infant age, race/ethnicity, calendar time, and season.
Among 3,815 ARI encounters in infants, 455 (12%) tested positive and 3,360 (88%) tested negative for influenza; 69 (15%) cases vs 1,018 (30%) controls were born to mothers who received an influenza vaccine in pregnancy. Overall VE was 53 (95% CI: 38–64). VE was statistically significant among infants 0–1 month (64%, 95% CI: 40–80), 2-3 months (63%, 95% CI: 39–79), and third trimester maternal vaccination (70%, 95% CI: 56–81). VE was not statistically significant among infants 4-5 months (34%, 95% CI: -1–58), first (29%, 95% CI: -13–57), and second trimester vaccination (25%, 95% CI: -19–55).
Maternal influenza vaccination was effective against influenza-associated ED/UC encounters in infants <6 months. VE point estimates were highest in those 0–3 months and when vaccinated in the third trimester. These findings provide evidence of infant protection from maternal influenza vaccination and may help inform clinical decisions about timing of influenza vaccination during pregnancy.
