Sat Dec 27 10:40:00 UTC 2025: News Article:
Aggressive Flu Strain, Subclade K, Drives Early Severity in U.S. Flu Season
NEW YORK – A new, highly contagious and aggressive strain of influenza A H3N2, known as subclade K, is rapidly spreading across the United States, contributing to a more severe flu season, according to the Centers for Disease Control and Prevention (CDC).
The World Health Organization (WHO) has identified the K variant as a significant evolution of influenza A (H3N2) viruses, with a CDC report revealing that nearly 90% of influenza A(H3N2) viruses collected since late September belong to this subclade.
Experts say the K variant causes more intense flu symptoms, including fever, chills, headache, fatigue, cough, sore throat, and runny nose.
“It’s becoming evident that this is a pretty severe variant of the flu,” said Dr. Neil Maniar, professor of public health practice at Northeastern University, in an interview. “Certainly, in other parts of the world where this variant has been prevalent, it’s caused some severe illness, and we’re seeing an aggressive flu season already.”
The CDC estimates that this flu season has already resulted in at least 4.6 million illnesses, 49,000 hospitalizations, and 1,900 deaths. While the CDC releases weekly reports tracking respiratory illness activity by state, people should not be alarmed if medical visits are high in their state, as this is not necessarily representative of confirmed cases of influenza.
Experts, including Dr. Maniar, suggest that the combination of the aggressive subclade K strain and lower vaccination rates has created a “perfect storm” for a severe flu season. “We’re going in [to this flu season] with lower vaccination rates and a variant that in itself seems to be more aggressive,” Dr. Maniar added.
While it’s uncertain whether this year’s flu vaccine directly addresses the subclade K mutation, health officials urge people to get vaccinated. The CDC recommends the flu vaccine as the best line of defense against the virus.
Dr. Maniar emphasized that it is not too late to get vaccinated, as peak flu season has not yet arrived. “The vaccine still provides protection against serious illness resulting from the subclade K variant that seems to be going around,” he said. “There are likely to be lots of indoor gatherings and other events that create risk of exposure, so protection is important.”
Individuals typically start to develop some degree of protection within a few days and gain the full benefit within about two weeks, so now is the time for anyone who hasn’t gotten the vaccine yet.
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