How well did the flu vaccine work last winter?
Last winter a new H3N2 strain, subclade K, arrived early. UKHSA’s data shows how much protection the vaccine still gave, and what that means for this season.
In short: despite a mismatched H3N2 strain, UKHSA’s early 2025/26 estimates showed the vaccine cut the chance of needing hospital care from flu by around a third in working-age adults and by around three quarters in children.
What was different about the 2025/26 season?
Flu arrived early in England in autumn 2025. Most cases were influenza A(H3N2), and a large share belonged to a newly emerging group of viruses known as subclade K. Laboratory testing by UKHSA found these viruses reacted much less well with antibodies raised against the season’s vaccine strain, which led to concern that the vaccine would offer little protection.
What did the real-world data show?
On 11 November 2025 UKHSA published early estimates of how well the vaccine prevented people from needing emergency care or hospital admission with flu. Compared with unvaccinated people, protection was estimated at:
| Age group | Estimated protection against hospital attendance |
|---|---|
| Children aged 2 to 17 | about 75% |
| Adults aged 18 to 64 | about 33% |
| Adults aged 65 and over | about 35% |
The full analysis, published in Eurosurveillance later that month, reported similar ranges: 72 to 75% in children and 32 to 39% in adults. Dr Jamie Lopez Bernal, UKHSA’s consultant epidemiologist for immunisation, described the results as reassuring evidence that the vaccines offered important protection despite the new subclade.
How should an employer read a figure like 33%?
Vaccine effectiveness is a reduction in risk, not the proportion of people who are protected outright. A figure of about a third means vaccinated adults were roughly a third less likely to need hospital care for flu than similar unvaccinated adults, in a season when the circulating strain had drifted away from the vaccine. In better-matched seasons effectiveness is often higher. Early-season estimates can also change as more data comes in.
The practical point for workplaces is that flu vaccination reduces risk rather than removing it. Staff who are vaccinated can still catch flu, but the NHS notes that illness is likely to be milder and shorter.
What changes for 2026/27?
Every year the World Health Organization recommends which strains vaccines should target, and the UK’s Joint Committee on Vaccination and Immunisation (JCVI) advises on which vaccines to use. For 2026/27 the preferred vaccines listed in England’s national programme letter are all trivalent, covering two influenza A strains and one influenza B strain. Your pharmacy will confirm the exact product for a private workplace clinic.
Read the 2026/27 employer briefing · Plan a clinic day
Sources
Let’s plan your workplace clinic.
Tell us your location, likely attendance and preferred dates.
Request a quote