What are 2025 influenza vaccine effectiveness estimates against hospitalization by age group?
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Executive summary
Interim real‑world estimates for the 2025 influenza vaccine’s protection against hospitalization cluster by age: children and adolescents show strong protection in some datasets (~63%–78% and 72%–75% in early England data), while adults show moderate protection with wider variation (roughly 30%–55%, depending on age and study) [1] [2] [3] [4]. Southern Hemisphere 2025 surveillance and pooled U.S. network estimates both support the conclusion that vaccines are reducing hospitalizations substantially overall but that effectiveness varies by age group and study design [4] [5].
1. Children and adolescents — generally high protection, but not uniform
Multiple early analyses report strong vaccine effectiveness (VE) against influenza‑associated hospitalization for children and adolescents: two U.S. VE networks estimated VE at 63% and 78% against hospitalization in pediatric groups during the 2024–25 data capture that informed 2025 assessments [1], and an early England analysis reported VE around 72%–75% for emergency‑department visits and hospital admissions among those under 18 in late‑2025 observations [2]. By contrast, pooled Southern Hemisphere SARI data for 2025 showed lower pediatric hospitalization VE (~51.3% among young children), illustrating that estimates depend on circulating viruses, regional surveillance methods, and timing [4]. All sources, however, converge on a clear point: vaccination substantially reduces the risk of pediatric hospitalization from influenza this season, even where point estimates vary [1] [4] [2].
2. Working‑age adults (roughly 18–64) — moderate, more consistent benefit
Interim U.S. network reports place adult hospitalization VE in a moderate band, commonly between about 41% and 55% overall, with adult 18–64 estimates leaning toward the higher end (approximately 48%–51% in some network analyses) [5] [3]. The England analysis grouped all adults at 32%–39% for ED attendance/hospital admission, but its subtype‑specific signals suggested higher point estimates for adults 18–64 against A(H3N2) with wide confidence intervals, underscoring statistical uncertainty [2]. Southern Hemisphere pooled data also reported roughly half of severe outcomes averted among priority adult groups, supporting the middle‑of‑the‑road conclusion that adult vaccination provides meaningful but incomplete protection against hospitalization [4].
3. Older adults (≥65) — smaller, variable protection; high‑dose and enhanced products matter
Effectiveness estimates for older adults are the most variable: U.S. networks reported hospitalization VE in older adults from about 38% up to 57% across certain estimates [3], while Southern Hemisphere data found lower VE (~37.7% in older adults) [4]. Randomized and registry studies, and practice guidance, point to improved protection when high‑dose or enhanced vaccines are used for older adults versus standard doses, suggesting product choice influences observed VE in this age group [6] [7]. The NEJM and ACP literature note that enhanced formulations can yield better prevention of severe outcomes in older adults, an important caveat when interpreting crude age‑stratified VE numbers [6] [7].
4. Why estimates differ — surveillance, circulating strains, and study design
Differences across the U.S. VE networks, the England study, and Southern Hemisphere surveillance reflect variation in endpoints (hospitalization vs. ED visit plus admission), circulating virus mix (H1N1, H3N2 subclades, or influenza B), timing of measurement, and analytic methods, including adjustments for confounders and vaccination definitions [1] [4] [2] [8]. For example, England’s early 2025–26 work emphasized A(H3N2) subclade K activity and still found typical VE ranges for children and adults, whereas the Southern Hemisphere pooled SARI data reported lower VE in older adults but higher VE against influenza B [2] [4]. These methodological and virologic differences explain much of the apparent spread in point estimates.
5. Bottom line and practical implication
Across multiple interim and regional analyses for 2025, influenza vaccination consistently reduces the risk of influenza‑associated hospitalization: children generally show the strongest protection (point estimates often >60% in some studies; 50% in others), adults show moderate protection (commonly ~40%–55% for working‑age adults), and older adults show variable, often lower estimates that can be improved with high‑dose or enhanced vaccines [1] [4] [2] [3] [6]. Surveillance will continue to refine these numbers through the season, but the convergent message from CDC networks, Southern Hemisphere surveillance, and England analyses is that vaccination remains an effective tool to reduce hospitalizations across age groups [5] [4] [2].