A new Super Flu strain is spreading across several parts of the world, prompting a warning from the United States Centres for Disease Control and Prevention.

In a statement, the CDC disclosed that the newly mutated and fast-moving variant of influenza A, known as H3N2 subclade K, has become dominant in several Northern Hemisphere countries, heightening concerns over a potentially severe 2025–2026 flu season.

The agency explained that the variant was first detected in Europe after the current season’s flu vaccines had already been selected, and that it carries seven new mutations which scientists believe may enable it to evade immunity provided by existing flu shots.

The strain has already driven early and severe flu seasons in Japan and the United Kingdom and is now spreading widely in Canada, where experts have warned 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 accounts for the vast majority of analysed H3N2 samples, even though overall flu activity has yet to reach its peak.

According to CDC estimates, at least 4.6 million influenza cases have been recorded so far this season, with approximately 49,000 hospitalisations and more than 1,900 deaths reported.

Laboratory findings indicate that the overwhelming majority of characterised H3N2 viruses belong to the subclade K group, underscoring how dominant the variant has become among circulating strains.

CDC genetic surveillance further shows that subclade K has dominated most H3N2 samples analysed in recent weeks, although precise global case figures specifically linked to the variant are not yet systematically reported.

Public health officials, particularly within the United States Department of Health and Human Services, have expressed heightened concern because H3N2 viruses have historically been associated with more severe illness, especially among older adults and young children.

Monitoring efforts have also been affected by recent disruptions in CDC surveillance activities during a government shutdown, which has limited real-time tracking of the virus’s spread.

Despite worries about mutation and potential vaccine mismatch, experts continue to stress that flu vaccination remains essential, noting that while protection against subclade K may be reduced, current vaccines still provide substantial protection against severe illness, hospitalisation, and death, and remain effective against H1N1 and influenza B strains that are also circulating.

Health officials said symptoms linked to the new variant are similar to those of typical influenza A, including sudden fever, chills, body aches, headaches, severe fatigue, congestion, runny nose, and cough.

They noted that these symptoms overlap with those of COVID-19 and other respiratory infections, prompting clinicians to recommend testing, including the use of at-home “3-in-1” rapid tests capable of detecting flu A, flu B, and COVID-19.

As the virus continues to spread and flu season intensifies, experts have warned that vigilance, vaccination, and early testing will be crucial in limiting the impact of what could become an especially severe flu season.