Aggressive new flu variant drives global surge, doctors warn of severe symptoms

An aggressive new flu variant, subclade K of Influenza A H3N2, is driving a global surge in infections, including in the United States, health officials say. Early signals point to more severe symptoms compared with recent flu seasons, triggering warnings that this could be a difficult season for hospitals and families alike.

The World Health Organization described subclade K as "a notable evolution" of influenza A (H3N2) viruses, complicating the match with this year's vaccine. Some experts say the vaccine may be less protective against this mutation, though health officials stress that vaccination remains important to reduce hospitalizations and severe illness. Dr. Neil Maniar, professor of public health practice at Boston’s Northeastern University, told Fox News Digital that the new strain is already causing severe illness in other parts of the world and may portend a challenging season. "The vaccine is very important to get, but because it's not perfectly aligned with this variant, I think that's also contributing to some degree to the severity of cases we're seeing," he said. "We're going in [to this flu season] with lower vaccination rates and a variant that in itself seems to be more aggressive." Another concern, he added, is that the season could see a high number of cases overall and a higher proportion of those cases becoming severe.

The variant appears to differ from prior strains in a way that heightens classic flu symptoms, including fever, chills, headaches, fatigue, cough, sore throat and a runny nose. Health officials describe subclade K as the "perfect storm" for an aggressive flu season, given the mutation’s novelty and the now-lower level of population immunity. There is particular worry among clinicians that people who contract this strain may experience more rapid progression to severe illness, especially among older adults and those with underlying conditions. "There’s a lot of concern that this could be a particularly difficult flu season, both in terms of the total number of cases and the severity of those cases," Maniar said.

Because subclade K is quite different from prior variants, experts say there is less natural immunity at the community level, further increasing the risk of spread and severity. Those who are unvaccinated remain at heightened risk for severe symptoms and hospitalization, according to the doctor. In addition to vaccination, public health guidance emphasizes frequent hand washing and proper hygiene. While flu can spread through the air, others illnesses such as norovirus can persist on surfaces for up to two weeks, underscoring the importance of cleaning surfaces and practicing respiratory etiquette. The holiday season, with gatherings and crowded transportation, can amplify exposure to circulating viruses.

For those who are not feeling well or who suspect they have flu symptoms, staying home is strongly advised to reduce transmission. If you are unsure about your health status or diagnosis, see a healthcare provider for testing. Some providers may prescribe antiviral medications to shorten illness and reduce the risk of complications. It is important to remain vigilant and protect yourself and your family through vaccination, hygiene and avoiding contact with others when sick.

Health officials emphasize that the best defense remains vaccination when available, even if the vaccine isn’t perfectly matched to subclade K. Hospitals and clinics are monitoring the situation closely as winter spreads across hemispheres. The best approach is to seek timely care, test when advised, and follow public health guidance during this evolving outbreak.