What is the new H3N2 flu strain causing outbreaks?

The new H3N2 flu strain has acquired 7 new mutations, making it quite different from the H3N2 virus included in this year's flu vaccine.

How is the UK affected by the new H3N2 flu strain?

The UK is heading into what the head of the National Health Service calls a "cruel winter", with flu cases triple what they were last year.

How is Japan impacted by the new H3N2 flu strain?

Japan is experiencing an "unprecedented" early and harsh flu season, with flu cases in Tokyo surging to nearly six times the level seen at the same time last year.

Home / Health / Flu Vaccine May Offer Limited Protection Against Rapidly Spreading H3N2 Variant

Flu Vaccine May Offer Limited Protection Against Rapidly Spreading H3N2 Variant

13 Nov

•

Summary

New H3N2 flu strain causing outbreaks in Canada, UK, and Japan
Strain has acquired 7 new mutations, making it different from vaccine
UK heading into "cruel winter" with flu cases triple last year
CDC data limited due to government shutdown and layoffs

Flu Vaccine May Offer Limited Protection Against Rapidly Spreading H3N2 Variant

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.