What’s Going On with Flu This Winter (2025-2026 Season)?
As of late December 2025, the 2025-2026 flu season in the United States is ramping up significantly, with influenza activity increasing nationwide just as holiday gatherings peak. While it’s still early in the typical peak period (usually December-February), indicators show a sharper rise than recent years at this point, driven by a dominant, mutated strain that’s raising concerns about potential severity.
Current Activity and Trends
- Rapid Increase: Flu is spreading in most parts of the country, with sustained elevated activity in many areas. Positive test rates jumped from around 8% to nearly 15% in early December, and outpatient visits for flu-like illness are above baseline levels.
- Hospitalizations on the Rise: Cumulative lab-confirmed flu hospitalizations reached about 3,800-4,000 by mid-December (per FluSurv-NET data covering ~9% of the U.S.), with weekly rates climbing to 3.5 per 100,000 population. CDC estimates at least 4.6 million illnesses, 49,000 hospitalizations, and 1,900 deaths so far this season.
- Regional Hotspots: High or very high activity in states like Colorado, Louisiana, New Jersey, New York, and parts of the Southeast/Mid-Atlantic. Overall severity indicators remain low for now, but experts warn of a potentially “pretty severe” season ahead.
- Pediatric Impact: Three flu-related child deaths reported so far, a somber early sign.
Compared to last season (2024-2025, classified as high severity), this one started similarly timed but is showing faster escalation in some metrics.
Dominant Strain: H3N2 Subclade K
The big story this winter is influenza A(H3N2) subclade K, a mutated variant that’s dominating globally and in the U.S. (making up ~90% of characterized H3N2 viruses).
- It emerged late, causing a partial mismatch with the 2025-2026 vaccine’s H3N2 component.
- H3N2 seasons historically hit harder, especially on older adults and young children, with higher hospitalization rates.
- Early data from the UK shows the vaccine still 30-40% effective in adults and 70-75% in kids against hospitalization—meaning it reduces severity even if not preventing all infections.
No evidence yet of dramatically increased severity beyond typical H3N2 patterns, but vigilance is high.
How Flu Compares to COVID and RSV
This winter’s “tripledemic” threat is real but uneven:
- Flu: Leading the pack right now with sharp rises.
- COVID-19: Circulating at relatively low levels compared to prior winters—no major surges yet.
- RSV: Trending upward in the Southeast/South/Mid-Atlantic, especially among young kids (increasing ED visits/hospitalizations), but overall low nationally.
Combined peak hospitalizations for the three could match last season’s levels, per CDC outlook.
Prevention Tips
- Get Vaccinated: It’s not too late—flu shots still offer solid protection against severe outcomes, even with the mismatch.
- Basics Work: Handwashing, masking in crowds if high-risk, staying home when sick, and testing for accurate treatment (antivirals like Tamiflu work best early).
- High-Risk Groups: Elderly, young children, pregnant people, and those with chronic conditions should be extra cautious.
Flu seasons are unpredictable, but current data points to a robust one ahead—stay informed via CDC’s FluView for weekly updates. If symptoms hit (fever, cough, body aches), test and treat promptly.
In this active winter respiratory season, flu is the one to watch closely right now, with potential for a challenging peak in January-February.