A new Super Flu strain is spreading globally, the US Centres for Disease Control and Prevention has warned.

In a statement, the agency said the newly mutated fast-moving variant of influenza A, known as H3N2 subclade K, has become dominant in multiple Northern Hemisphere countries, raising concern about a potentially severe 2025–2026 flu season.

First detected in Europe after the season’s flu vaccines were selected, the variant carries seven new mutations that scientists say may help it evade immunity from current flu shots.

The strain has already fuelled early and severe flu seasons in Japan and the United Kingdom and is now circulating widely in Canada, where experts warn of a possible mismatch between the vaccine’s H3N2 component and the emerging variant.

In the United States, genomic sequencing and surveillance data show that H3N2 subclade K is already present in most states and now makes up the vast majority of analysed H3N2 samples, even though overall flu activity has not yet peaked.

According to CDC estimates, at least 4.6 million cases of influenza have been reported so far this season, with about 49,000 hospitalisations and over 1,900 deaths reported.

Laboratory data show that the vast majority of H3N2 viruses characterised belong to the subclade K group, showing how dominant the variant has become among circulating strains.

CDC genetic surveillance shows subclade K dominating most H3N2 samples analysed in recent weeks, although precise global case counts specifically for this variant are not systematically reported publicly yet.

Public health officials, particularly in the US Department of Health and Human Services, are particularly concerned because H3N2 viruses are historically linked to more severe illness, especially among older adults and young children.

Further, it was gathered that monitoring efforts have also been complicated by recent disruptions in CDC surveillance during the government shutdown, limiting real-time tracking of the virus’s spread.

Despite concerns about mutation and vaccine mismatch, experts strongly emphasise that flu vaccination remains critical, while protection against subclade K may be reduced, the current flu shot still offers substantial defence against severe illness, hospitalisation, and death, and continues to provide good coverage against H1N1 and influenza B strains that are also circulating.

Health officials say symptoms of the new variant resemble typical influenza A, including sudden onset of fever, chills, body aches, headache, profound fatigue, congestion, runny nose, and cough.

These symptoms, they note, overlap with COVID-19 and other respiratory infections, and so clinicians are urging testing, including the use of at-home “3-in-1” rapid tests that can detect flu A, flu B, and COVID-19.

As the virus spreads and flu season intensifies, experts warn that vigilance, vaccination, and early testing will be key to limiting the impact of what could become a particularly harsh flu season. (Vanguard)