• Posted November 20, 2025

New Flu Variant Could Bring Another Severe U.S. Season

A new flu variant spreading overseas may set the stage for another tough winter in the United States, experts warn.

The strain, called subclade K, has caused a rise in flu cases in the United Kingdom, Canada and Japan. And now signs suggest it is beginning to take hold across the United States as flu activity rises.

According to the latest U.S. Centers for Disease Control and Prevention (CDC) FluView report, reported flu activity in the United States remains low but is climbing quickly.

Last year’s flu season was the worst the United States had seen in nearly 15 years and led to at least 280 child deaths, according to the CDC.

Most cases this year are from the H3N2 virus and about half of those belong to the subclade K variant, the same strain that fueled a difficult flu season in the Southern Hemisphere.

Because it wasn’t circulating widely when strains were selected for the vaccine update, this year’s flu shot targets close strains of the virus.

"It’s not like we’re expecting to get complete loss of protection for the vaccine, but perhaps we might expect a little bit of a drop-off if this is the virus that sort of dominates the season, and early indications are that’s probably going to be the case," Richard Webby, a researcher at St. Jude Children’s Research Hospital in Memphis, Tennessee, told CNN.

Early findings from the UK Health Security Agency suggest the variant carries seven genetic changes on a major part of the virus, making it a bit harder for the body's immune system to recognize.

Even so, they found that the flu shot has reduced the risk of hospitalization or emergency care by about 75% in children and 30% to 40% in adults so far this season.

What worries experts even more is that fewer Americans appear to be getting the flu shot.

Data from IQVIA shows that pharmacies gave 26.5 million flu vaccinations from August through October, down from 28.7 million during the same period last year.

"I’m not surprised," Jennifer Nuzzo, professor of epidemiology and director of the Pandemic Center at Brown University in Providence, Rhode Island, said.

She said recent debates about vaccine safety have "left people confused but possibly at the worst have left people worried about getting vaccinated."

Australia’s flu shot rates also fell this year and the country went on to record more than 443,000 cases.

"What they saw in Australia is that they had a bad season. And so it’s concerning for you and us, what’s coming," Dr. Earl Rubin, division director of infectious disease at Montreal Children’s Hospital, told CNN.

Several early indicators already show flu levels rising in the U.S.

The WastewaterSCAN network found type A flu in 40% of samples in November, up from 18% in October, according to Marlene Wolfe, an assistant professor in the department of environmental health at Emory University in Atlanta.

Only four U.S. monitoring sites in Maine, Vermont, Iowa and Hawaii have officially crossed the threshold for declaring flu activity high, but experts say the trend is clear.

While it’s not yet clear whether subclade K could cause more severe illness, a rise in infections alone could cause hospitalizations to skyrocket, Rubin noted.

"It’s not too late. Go and get your flu shot," Dr. Adam Lauring, chief of the division of infectious diseases at the University of Michigan Medical School, in Ann Arbor, said.

These results are preliminary and have not yet been peer-reviewed.

More information

The Texas Department of State Health Services (DSHS) has more on the flu vaccine.

SOURCE: CNN, Nov. 18, 2025