As the United States wraps up the holiday season on December 27, 2025, influenza cases are skyrocketing nationwide, marking one of the most intense starts to flu season in recent years. A new variant of the influenza A(H3N2) virus, known as subclade K, is driving much of the surge, raising concerns about vaccine effectiveness while co-circulating with other respiratory illnesses like COVID-19 and RSV.
New York State has been particularly hard-hit, reporting a record-breaking 71,123 laboratory-confirmed flu cases for the week ending December 20—a 38% increase from the previous week and the highest single-week total ever recorded. Hospitalizations in the state also spiked, with 3,666 flu-related admissions that week, surpassing peaks from last winter. State Health Commissioner Dr. James McDonald noted that the season is “more severe in New York this year, and we’re not even close to the peak yet.” Holiday gatherings, he added, are likely accelerating spread by mixing “love and joy” with germs.
Nationwide, the Centers for Disease Control and Prevention (CDC) reports rising flu activity in nearly every state. As of mid-December, infections were increasing or likely growing in 47 states, with only Hawaii seeing a decline. The CDC estimates at least 4.6 million illnesses, 49,000 hospitalizations, and 1,900 deaths from flu so far this season, including three pediatric deaths.
States with “very high” or “high” influenza-like illness activity include Colorado, Louisiana, New York, New York City, and several others in the Northeast and South. Emergency room visits for flu have climbed sharply in places like Colorado (up 7%), Louisiana (7% of visits), and New York City (nearly 9%).
The dominant culprit is subclade K, a mutated form of H3N2 that emerged after this year’s vaccine was formulated. It has caused outbreaks in Japan, the U.K., Canada, and Europe before becoming prevalent in the U.S. Experts like Andrew Pekosz from Johns Hopkins say it’s unclear if this variant causes more infections or severe illness, but cases are clearly rising and expected to continue into the new year.
Adding to the challenge is a drop in vaccination rates. Over 47.6 million flu shots have been administered this season at pharmacies and doctors’ offices—about 3 million fewer than last year. Jennifer Nuzzo from Brown University warns this could lead to a particularly tough season.
Typical flu symptoms remain the same: fever, cough, runny nose, fatigue, muscle aches, and chills.
Health officials emphasize it’s not too late to get vaccinated—the shot still offers protection against severe outcomes, even if it’s not a perfect match for subclade K. Everyone 6 months and older is recommended to get it.
Other key prevention steps include:
- Frequent handwashing with soap for at least 20 seconds
- Avoiding touching eyes, nose, and mouth
- Staying home when sick
- Covering coughs and sneezes
- Disinfecting surfaces
- Wearing high-quality masks (like N95 or KN95) in crowded indoor spaces if you’re at higher risk
For those who get sick, especially children, older adults, or people with underlying conditions, antiviral medications can shorten illness and reduce complications if started within 48 hours of symptoms.
As flu activity is expected to peak in the coming weeks, experts urge vigilance. “It is gonna get worse before it gets better,” McDonald said of New York’s outlook, a sentiment echoing across the country. Staying informed and taking simple precautions can help mitigate the impact of this challenging season.
