Flu Season Surges: Experts Unpack Why This Year Is So Severe

Daily Health

19/01/2026

The United States is experiencing one of its most severe flu seasons in decades, with millions falling ill, hundreds of thousands hospitalized, and thousands of deaths, including children. Experts point to a new, rapidly evolving strain of influenza A, dubbed "subclade K," as a primary driver of the heightened activity.

Key Takeaways

This flu season is among the worst in nearly 30 years, with high case numbers and hospitalizations.
A new flu variant, "subclade K" (a subtype of A(H3N2)), is dominant and evades existing immunity more effectively.
While subclade K is highly transmissible, it does not appear to cause more severe illness than other strains.
Flu vaccination is still recommended, though the vaccine may be a less perfect match for subclade K.
Lower vaccination rates this year are contributing to the severity.

Understanding Subclade K

Flu viruses constantly evolve, and scientists track these changes using a classification system that identifies types, subtypes, clades, and subclades. This year, the dominant strain is influenza A(H3N2), with over 91% of identified samples belonging to a new group called subclade K. This subclade possesses distinct mutations that make it less recognizable to the human immune system, allowing it to spread more easily and leading to increased infections and hospitalizations.

Is Subclade K a "Super Flu"?

Despite its high transmissibility, subclade K is not considered a "super flu." Current data indicate that it does not cause more severe disease or deadlier outcomes than other circulating flu strains. Symptoms remain typical for influenza, including fever, cough, body aches, and fatigue, with potential complications like pneumonia and sepsis in severe cases. High-risk groups, including the elderly, young children, pregnant individuals, and those with chronic health conditions, remain most vulnerable to severe complications.

Flu Vaccine Effectiveness and Uptake

The current flu vaccine may offer reduced protection against subclade K compared to previous seasons, but experts emphasize that it remains crucial for preventing serious illness and complications. Data from the Southern Hemisphere suggests the vaccine still significantly reduces hospitalization risks. However, vaccination rates have declined this year, particularly among children, with only about 42% of U.S. children vaccinated so far. This lower uptake is a significant factor contributing to the season's severity, as a large proportion of flu-related deaths in previous seasons occurred in unvaccinated individuals.

Prevention and Treatment

It is not too late to get vaccinated, and health officials strongly recommend it, especially for high-risk individuals. Beyond vaccination, other protective measures include wearing masks in crowded indoor spaces, improving ventilation, staying home when sick, and practicing good hand hygiene. Antiviral medications, such as Tamiflu, are available and effective in reducing symptom severity and duration, particularly when administered early. Subclade K has shown responsiveness to standard antiviral treatments.

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