An unusual and aggressive strain of influenza has hit parts of the U.S., prompting flu season to begin two and a half months earlier than usual in some places. According to the Centers for Disease Control and Prevention (CDC) emergency room visits for influenza-like illnesses have tripled across the country, compared to the same period last year.
Dr. Alex Greninger, head of the Division of Infectious Disease Diagnostics at the University of Washington’s Department of Laboratory Medicine, told CNN on October 22, 2026, that unlike the usual spread of the flu, this strain has started on the West Coast, including in Washington state.
“We’re basically seeing January levels of flu in the last week,” he told the outlet, noting that flu season typically starts in the South, arriving in Florida from the Southern Hemisphere, and then starts to spread north.
CNN reported that, according to last week’s data from Washington’s Department of Public Health, one in 10 people in that state who were tested for the flu tested positive. Greninger said that’s equivalent to “January levels of flu.”
The CDC was already noticing a significant rise in flu cases in all 50 states in early October, reporting the highest activity in Arizona, California, Hawaii, Nevada, Alaska, Idaho, Oregon and Washington, per USA Today. Meanwhile, research from Stanford University showed it’s the earliest flu season in at least four years.
Greninger told CNN that the wave of flu hitting the Western states came from Asia and “is dominated by the H1N1 virus,” the culprit behind 2009’s flu pandemic. But this strain also has a gene mutation, called G155E, that makes the virus better at breaking through built-up immunity in people.
The strains used to create this year’s flu shots were chosen in the spring, before this new variant had become a threat, per CNN. Still, getting the vaccine is a far better defense than not getting the vaccine, Greninger said.
“A lot of people, like even myself, would wait until late October, which we’re sort of in already,” he said. “But really, the time to get vaccinated was actually two to three weeks ago.”
Dr. Jennifer Duchon, a pediatric infectious disease expert at Mount Sinai Children’s Hospital in New York, told Reuters that there’s concern within the medical community that “the H1N1 strain this year hasn’t been seen by a lot of younger folk, so it may be more severe to them.”
Even in children, the flu can be deadly. In 2025, Reuters reported, an estimated 32 million Americans came down with a case of the flu. Of those, 390,000 were hospitalized, and 24,000 died. According to stats from data firm IQVIA, the outlet said, the number of vaccines American adults received was down more than 20% compared to the previous year.
Flu symptoms usually come on suddenly, per the CDC. Symptoms often include a fever, feeling feverish, or having the chills. Other common signs are a cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue/tiredness. Some people may experience vomiting and diarrhea, but that’s more common in children than adults.
Flu Season Hits U.S. Early Due to Mutated Virus: Where It’s Worst Right Now