Which age groups show the highest or lowest vaccine effectiveness against 2025-2026 H3N2?
Executive summary
Early real-world data from the UK show the 2025–26 vaccine is reducing hospital attendance for children aged 2–17 by roughly 70–75% and protecting adults at substantially lower levels—about 30–40% against severe endpoints so far (UKHSA/EuroSurveillance interim analysis) [1] [2]. Multiple public-health commentators warn H3N2 seasons typically give lower VE in older adults and that surveillance and vaccine-type choices (egg vs cell/recombinant, enhanced doses) matter for observed protection [3] [4].
1. What the numbers say: clear gap between children and adults
Interim vaccine-effectiveness (VE) estimates published by UKHSA and summarized in Eurosurveillance report VE of approximately 72–75% against emergency department attendance/hospital admission for children and adolescents (<18 years) and about 32–39% in adults during the autumn period dominated by H3N2 subclade K [5] [2]. The UK government press release and other outlets restate the same headline figures—70–75% in 2–17 year‑olds and 30–40% in adults—underscoring a consistent early-season signal from English surveillance [1] [6].
2. Why children appear to be better protected this season
UK investigators note the high VE in children aligns with historical observations that live-attenuated influenza vaccine (LAIV) and strong post-vaccination responses in younger immune systems can yield higher short‑term protection, even when the circulating virus has antigenic differences from the vaccine strain [5]. Media and public‑health summaries emphasize these results as encouraging because reduced paediatric hospital attendance may also indirectly protect other age groups via lowered transmission [1] [6].
3. Why adult protection is lower—and what that means
Experts and reviews point out that H3N2-dominant seasons have tended to produce lower vaccine effectiveness in adults, especially older adults, compared with other subtypes; antigenic drift, egg‑adaptation of vaccine viruses, and age-related immune decline contribute to that pattern [3] [7]. Interim VE in adults reported in England (≈32–39%) reflects this pattern and signals more remaining risk of severe illness for older adults and working-age adults than for children [2] [5].
4. How subclade K factors into the VE picture
Genetic and antigenic characterisation shows H3N2 subclade K (J.2.4.1) has diverged from the vaccine reference strains chosen earlier in 2025, and ferret antisera show reduced reactivity; however, real‑world VE against severe endpoints remains in typical ranges per the interim report [2] [5]. Public‑health agencies caution that laboratory serology (ferret or human antibody titres) is only one piece of the story—epidemiologic VE estimates determine actual protection against hospitalisation [6] [2].
5. Other data and perspectives—consistency and limits
Analysts in CIDRAP and policy briefs from ECDC note the same early UK findings while warning about uncertainty: H3N2 seasons often cause more severe disease in older adults and VE estimates can change as the season matures and more data accrue [3] [4]. The Medical Letter and independent outlets discuss vaccine formulation and enhanced-dose options for seniors but the provided sources do not supply new age‑stratified VE numbers beyond the UK interim results (available sources do not mention additional stratified VE estimates) [8] [9].
6. What to watch next—surveillance, vaccine type and confidence intervals
The interim report is just that—interim—and authors note confidence intervals are wider for some age groups and endpoints; ongoing surveillance in multiple countries will refine estimates [5] [2]. ECDC emphasizes that even with imperfect match, higher vaccine uptake in older adults correlates with lower disease burden, signaling that current vaccines still reduce severe outcomes at a population level [4].
7. Bottom line for readers and policymakers
Current, peer‑review–adjacent evidence from UK surveillance shows the largest protection this season is in children (70–75% against hospital attendance) and substantially lower protection in adults (~30–40% against similar endpoints) [1] [2]. Public‑health actors and clinicians should treat these as provisional estimates, continue to promote vaccination—especially in high‑risk groups—and monitor forthcoming VE updates and hospitalisation trends to guide messaging and resource allocation [5] [4].
Limitations: these conclusions rely on early-season, England‑focused VE analyses and lab characterisation; pooled, mature season estimates from multiple countries are not yet available in the provided reporting (available sources do not mention pooled global VE estimates beyond the cited UK/Europe reports) [5] [2].