Some are mild, while others—like last year—barrel through like a tornado. Every year, scientists do their best to predict what type of influenza virus will hit the US based on data from countries in the Southern Hemisphere whose flu seasons come earlier than ours. The key word here is predict.
Since the influenza virus mutates quickly, it’s hard for scientists to give a 100 percent guarantee that what’s ravaging Australia will also come for the US. That’s what happened in the brutal flu season last year—and this year. A few weeks ago, scientists gave a forecast of H3N2 (that’s the one dubbed “Super-K”) as the dominant flu strain for the US.
But early surveillance in flu cases from the West Coast found that a different type—Influenza A virus subtype H1N1—has overtaken H3N2 as the dominant flu strain in October. The CDC also released new flu data reporting a spike in flu-related hospitalizations. Does H1N1 sound eerily familiar?
H1N1 is also known as swine flu—a strain that sparked a pandemic back in 2009. So far, researchers have linked early flu ER visits to a mutation in H1N1 (a G155E mutation) that changes the way the virus attaches to and infects cells. Past research has found antibodies from past H1N1 infections or vaccinations may not recognize it, especially in younger populations.
In other words, there is a chance the mutated influenza virus could evade some pre-existing immunity. Here is what you need to know about this early jump to flu season and how to best protect yourself against this mutated strain. HERE’S WHAT THE CDC learned: In mid-October this year, the agency saw 10 times more hospitalizations for flu than it did in 2025 (2.1 hospitalizations per 100,000 people compared to 0.2 per 100,000 during the same week last year).
Among other changes are when and where the virus is spreading. While influenza cases typically tick up around fall, infections began rising in August. The boost of early cases was mostly on the West Coast, including Arizona, Nevada, and California.
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