How effective was the 2024-2025 seasonal influenza vaccine in preventing hospitalisation in different age groups in the UK?
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Executive summary
The UK’s 2024–25 seasonal flu vaccination programme reduced the risk of hospital attendance and admission, with stronger protection in children than adults: early UKHSA analyses and media summaries report vaccine effectiveness against hospital attendance of about 70–75% in 2–17 year‑olds and roughly 30–40% in adults [1] [2] [3]. UK policy and JCVI reviews from 2024–25 stress that effectiveness varied by age, vaccine type and over time, and that the adult programme aims to limit hospitalisation especially in older and at‑risk groups [4] [5].
1. What the main numbers mean — big differences by age
UKHSA preprint summaries and contemporaneous reporting put interim vaccine effectiveness (VE) against hospital attendance in autumn 2025 at about 70–75% for children aged 2–17 and 30–40% in adults [1] [2] [3]. Those figures reflect reduced likelihood of attending hospital with influenza among vaccinated people versus unvaccinated people during early post‑vaccination months; the higher protection in children is repeatedly highlighted in UK reporting [1] [6].
2. Why children saw stronger protection
Children in the UK mostly received the live attenuated influenza vaccine (LAIV) in 2024–25, and UK guidance notes an estimated 56% VE against primary‑care attendances in 2–17 year‑olds for 2024–25 (the majority having received LAIV) and later reporting showed even higher protection against hospital attendance in autumn 2025 [7] [1]. UKHSA and public health communicators interpret high paediatric VE as important both to protect children themselves and to reduce onward transmission to vulnerable adults [1] [6].
3. Adults and older adults — mixed signals and vaccine types
JCVI and UKHSA analyses emphasise more nuanced results in adults, particularly older adults: unpublished UKHSA analyses showed overlapping confidence intervals for VE against hospitalisation among older adults across adjuvanted, high‑dose and recombinant inactivated vaccines in 2024–25, and published summaries caution that adult VE is generally lower than in children and may wane over time [4] [5]. Interim surveillance and media summaries place adult VE against hospital attendance in the 30–40% range in early 2025 reporting [1] [2].
4. The role of viral evolution and strain mismatch
Laboratory characterisation from England showed reduced reactivity of a newly circulating A(H3N2) subclade K with antisera raised against 2024–25 vaccine strains — a laboratory signal consistent with a degree of antigenic drift [8]. UKHSA and independent commentators stress that even when drift occurs the vaccine can still substantially reduce severe outcomes, though effectiveness against mild infection or against a poorly matched strain may be lower [9] [2].
5. Timing, waning and programme design
JCVI adjusted timing of adult vaccination (moving the adult programme start closer to season onset) because evidence suggested VE in adults can wane and closer timing preserves protection during peak circulation [5]. Policymakers also use VE against hospitalisation as a key metric when choosing which vaccines to recommend for older adults and at‑risk groups [4].
6. Impact beyond VE numbers — hospitalisations prevented
Modelling cited by JCVI estimates the influenza vaccination programme prevented roughly 100,000 hospitalisations in 2024–25, underscoring population‑level impact even when per‑person VE is modest [5]. That modelling complements VE point estimates by showing cumulative benefits of coverage across age groups.
7. Limitations, caveats and what the sources don’t say
The early VE estimates cited are interim and come from periods soon after vaccination when waning is minimal; authors and UKHSA note these results may change as the season progresses and as circulating strains shift [2] [1]. Available sources do not provide a full, final age‑stratified VE analysis for the whole 2024–25 season across hospitalisation endpoints in every UK nation — instead we have interim English analyses, JCVI reviews, and multi‑country interim reports [4] [10]. Confidence intervals and specific subgroup data (for example by comorbidity or vaccine brand in younger adults) are not reported in the summary materials provided here [4] [5].
8. Bottom line for readers
Public‑health authorities in the UK conclude that the 2024–25 programme substantially reduced severe outcomes, especially in children, and that vaccination remains the best available tool to lower chances of hospital attendance and admission [1] [9] [5]. Critics and independent scientists point to antigenic drift (subclade K) and potential waning as reasons to interpret early VE cautiously and to maintain high uptake and timely administration [8] [2].
If you want, I can extract the specific interim VE estimates, confidence intervals and the original UKHSA preprint text for deeper scrutiny — or track whether final season‑wide VE reports with full age stratification have since been published.