Flu Season May Pack an Extra Punch

H3N2 linked to more severe illness, and now, there's a new variant spreading
Posted Nov 20, 2025 9:59 AM CST
Flu Season May Pack an Extra Punch
A sign for flu shots is displayed outside a Walgreens in Wheeling, Ill., Tuesday, Sept. 23, 2025.   (AP Photo/Nam Y. Huh)

Health experts are warning the upcoming flu season in the US could be particularly severe. Richard Webby, a flu researcher at St. Jude Children's Research Hospital, points to significant flu activity in the Southern Hemisphere, which often serves as a preview for the Northern Hemisphere's season. "The signs are, it could be a big season," Webby tells NPR, adding that the tail end of the Southern Hemisphere's season lasted longer than usual. According to the New York Times, "Australia experienced the worst flu season in its history." Then Britain's flu season began a month sooner than normal.

The current dominant strain in the Northern Hemisphere is H3N2, which triggers more severe illness than last year's dominant H1N1 stain, per the Times. The CDC estimates at least 38,000 deaths were tied to the flu last year. The dominant strain in the US is a new variant of H3N2, raising concerns that it is different enough to evade some protections from previous infections or vaccines. Caitlin Rivers, an epidemiologist at Johns Hopkins, tells NPR this year's flu shot "may not be as good a match as if we hadn't seen this new variant," but emphasizes that vaccines still provide significant protection, especially against severe illness.

Data from the UK suggests the current vaccine is 70% to 75% effective at preventing hospitalization in children and 30% to 40% effective at preventing hospitalization in adults. "We're likely a few weeks out from things getting really serious, and that means now is the time to get vaccinated, because it takes a couple of weeks for full protection," Sam Scarpino, a public health expert at Northeastern University, tells the Times. Flu activity is expected to rise through the holiday season as multigenerational families mix, potentially bringing the virus to unvaccinated members. (This new flu vaccine could be a "game changer.")

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