Health officials across the United States are warning people to be aware of a new “super flu” variant. Some states are even implementing mask mandates due to these spikes in influenza and other respiratory infections.
According to the Centers for Disease Control and Prevention (CDC) Weekly US Influenza Surveillance Report, the most frequently reported influenza viruses were influenza A(H3N2). However, multiple states are reporting a new variant of the flu known as “H3N2 Flu A Subclade K” is causing issues.
Dr. Thomas Russo, professor and chief of infectious disease at the University at Buffalo in New York, told Prevention Subclade K has several mutations that seem to make it more infectious.
In California, the Department of Health has warned this new flu variant is “causing an active, early flu season.” One flu outbreak in the Bay Area recently kept nearly a third of the students in one school district at home.
In New York, the Health Department reported nearly 10,000 emergency room visits for flu-like illness last week. It was the largest one-week spike in more than a decade.
In Iowa, an entire school district canceled classes due to a flu outbreak. An outbreak also forced a New Hampshire school to close.
A Georgia hospital has been restricting visitors due to flu. Some medical facilities in Indiana and Ohio have begun visitor restrictions. Major hospital systems in New Jersey have reinstated mask mandates. The state of New York is also requiring masks for unvaccinated healthcare workers.
“We think this Subclade K virus is evading population immunity, meaning more people are susceptible to infection,” Professor Andrew Pekosz with John Hopkins Bloomberg School of Public Health, told Fox News.
Influenza is spreading rapidly across the United States
Meanwhile, several other states including Colorado, Idaho, Louisiana, Maryland, Massachusetts, Michigan, New Mexico, North Carolina, Ohio, Rhode Island, South Carolina, and Wisconsin are experiencing high levels of flu activity.
“The flu came hard and the flu came early,” Dr. Stephen Ramirez of Stone Oak Family Practice in San Antonio, Texas told NBC News San Antonio. “This is our Christmas surprise. If you haven’t had it yet, be prepared because it’s coming.”
The CDC estimates that there have been at least 4,600,000 illnesses, 49,000 hospitalizations, and 1,900 deaths from flu so far this season. “Among 216 influenza A(H3N2) viruses collected since September 28, 2025, that underwent additional genetic characterization at CDC, 89.8% belonged to Subclade K,” the CDC wrote.
“It’s certainly widespread at this point and is putting people in the hospital,” Dr. Scott Roberts, head of infection prevention at Yale New Haven Hospital told CT Insider. “That’s not necessarily unique to this strain. There’s always going to be flu hospitalizations. But anytime there’s something that’s a little bit mutated from what we expect, it’s not a good thing.”