Health officials in the united Kingdom are investigating an early surge in influenza cases, driven by a newly identified strain of the H3N2 virus, dubbed “subclade K.” the variant is currently disproportionately affecting school-aged children, adolescents, and young adults, raising concerns about potential strain on healthcare systems as the winter season approaches. This H3N2 strain has undergone significant mutation, potentially reducing the effectiveness of this year’s flu vaccine, and prompting health agencies to closely monitor its spread and impact [[1]].
Health officials in the United Kingdom are on alert as cases of seasonal influenza are rising earlier than usual. The increase is driven by a particularly virulent strain of the H3N2 virus – referred to as a “subclade K” – which is primarily affecting school-aged children, adolescents, and young adults, according to the British Medical Journal (BMJ). Experts warn that the upcoming winter season could be one of the most severe the country has experienced in recent years.
The current circulating influenza A (H3N2) virus has acquired seven new mutations over the summer, meaning it’s significantly different from the H3N2 strain included in this year’s vaccine, explained Dr. Antonia Ho, a lecturer and infectious disease specialist at the University of Glasgow in Scotland. This change could allow the virus to evade immunity developed from prior infections or vaccinations, she noted.
H3N2 Poses a Greater Threat
The concern surrounding this strain stems from its tendency to cause more severe illness, particularly in older adults, compared to the H1N1 subtype. “For example, during the winter of 2022/2023, when A(H3N2) was dominant, there were 16,000 flu-associated deaths in the UK, compared to 8,000 last winter,” Dr. Ho added. This data highlights the potential for increased hospitalizations and severe outcomes with the current circulating strain.
According to the UK Health Security Agency (UKHSA), the flu season began five weeks earlier than usual in the UK. Currently, 84% of recent infections are linked to H3N2, with 87% belonging to the K subclade. Professor Adam Finn of the University of Bristol suggests a possible explanation is that population immunity controlling the spread of the flu is lower than normal, as cited by Gavi. An early start to the flu season is particularly concerning because many at-risk individuals may not yet have been vaccinated.
Vaccination Remains Beneficial
Experts predict this novel variant will be the dominant strain during the 2025-2026 flu season in the Northern Hemisphere. The question remains as to when and how extensively it will spread across Europe, including Switzerland, and the potential impact it may have. Despite not offering complete protection against the new strain, the flu vaccine remains a valuable tool. UKHSA data shows it prevents hospitalizations in 70 to 75% of cases among children aged 2 to 17, and in 30 to 40% of cases among adults. These findings suggest that vaccination can still significantly reduce the severity of illness and the burden on healthcare systems.
Eva Grau (egr) is a journalist at 20 minutes, a publication she joined in 2009. Her preferred topics are health and people-culture news.
