New variant could bring another severe flu season. Here's what to know

A new, highly contagious flu strain is spreading fast and it could mean we’re in for another severe season.

The strain, known as Subclade K, is already impacting countries like Canada, the UK and Japan with an increase in severe infections.

The Centers for Disease Control and Prevention says the variant has been detected in parts of the U.S. too, but so far flu activity remains low — that’s why the time to act is now.

“The flu vaccine is the best way to protect you and your family from getting the flu,” said Dr. Gabrina Dixon, a pediatrician at Children’s National Hospital. “[…] Based on years of data, flu normally rises in December, January. So if you get it now, it takes about two weeks for your immune system to build up, so this is a perfect time to get it.”

Dixon says that while this year’s flu vaccine is not a perfect match for Subclade K, it still offers strong protection against serious illness and hospitalization.

“I think of the immune system as like a great memory system, so it remembers things it’s been exposed to,” she said. “So when you get that flu vaccine, your body keeps a memory, like, ‘Hey, I have seen this before. I know how to protect you from this.’”

Subclade K is a mutation of the H3N2 strain, which typically causes more serious disease. Doctors say that coupled with lower vaccination rates could set the stage for another busy flu season.

“We want to decrease hospitalizations, we want to decrease people getting sick, and vaccines have been proven time and time again to do that,” Dixon said, “The science is there, the evidence is there, there’s no argument, it’s in the numbers. It works.”

As for symptoms, Subclade K appears similar to other flu strains, with people developing fever, chills, body aches and, in some cases, vomiting or diarrhea.

“For most people, you know, the flu can be managed at home,” Dixon said. “[…] Anytime they’re having a hard time breathing, and you feel like they’re not breathing right, make sure they go to the emergency room.”

Dixon said you should go see a doctor if:

• It’s been a prolonged illness.
• If you’re not getting better.
• If you’re dehydrated – which could look like not going to the bathroom as much or a baby using less diapers.
• If you’re not eating or drinking as much as usual.

Doctors say it’s especially important that kids are protected. Last season, 280 children died from the flu during the 2024-2025 season, according to the CDC, marking one of the most severe seasons here in over a decade.

“It’s a yearly vaccine for most people,” Dixon said. “Again, for infants, you can start at 6 months. For those who are less than 9 and it’s the first time ever getting the flu vaccine, you do get two doses that first year. But then again, it’s just a yearly dose.”

Health experts typically look to the Southern Hemisphere to get an idea of what it could mean for the U.S. flu season, and this winter, Australia recorded its worst flu season in history.

Bottom line: It’s not too late to get your flu shot, with cases in the U.S. expected to start rising after the holidays as more people travel and get together for family gatherings.