Mutated H3N2 Strain Fuels Severe Flu Outbreaks Across North America and Europe

As the 2025-2026 flu season gets underway, global health experts are increasingly concerned about a new, mutated strain of the H3N2 influenza virus that has emerged in recent months. This new H3N2 variant first appeared in June, four months after the composition of this year's flu shots had been finalized, and is now causing outbreaks in several countries.

In Canada and the UK, health officials are reporting an early and severe wave of flu cases driven by the new H3N2 strain. The UK's National Health Service chief has warned that the country is heading into a "cruel winter" with flu cases triple what they were last year. Similarly, Japan is experiencing an "unprecedented" early and harsh flu season, with a surge in cases in Tokyo that is nearly six times higher than the same time in 2024.

The new H3N2 strain has acquired 7 new mutations over the summer, making it quite different from the H3N2 virus included in this year's flu vaccine. As a result, the vaccine is expected to offer limited protection against the rapidly spreading variant.

While there are anecdotal reports of flu A cases across the US, the Centers for Disease Control and Prevention has not provided detailed national data since late September due to the ongoing government shutdown. Experts warn that the "hollowing out" of the CDC through layoffs could further delay the collection and analysis of critical flu surveillance data, leaving the US reliant on state and academic labs for insights.