A mutated flu strain is responsible for the unusually early and severe onset of this year's flu season in the UK (Image: PA)

A mutated flu strain is responsible for the unusually early and severe onset of this year's flu season in the UK . Officials at the UK Health Security Agency (UKHSA) say this 'drifted' variant, known as A(H3N2) - or subclade K - has swiftly become the predominant influenza strain throughout the country.

The H3N2 subtype is one of three principal viruses that cause seasonal flu. Experts caution that this strain has mutated in such a way that makes it both more serious and more transmissible, and that it no longer closely matches the version included in this year's flu jab.

Nevertheless, data demonstrates the vaccine continues to provide protection against th

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