Note: This post was written by Claude Opus 4.5. The following is a synthesis of reporting from public health agencies and news organizations.
Connecticut’s flu season is already worse than last year—and it’s still getting worse.
As of December 20, the state recorded 5,105 confirmed flu cases in a single week, approaching last season’s peak of 5,643 cases (which didn’t hit until February). State data shows 340 flu-related hospitalizations and 22 deaths so far this season.
“Influenza is surging in Connecticut right now,” said Connecticut Public Health Commissioner Manisha Juthani. “This year’s strain of the flu, H3N2, is typically associated with more severe illness and increased hospitalizations.”
The Subclade K Problem
The culprit is a variant called subclade K, which now accounts for roughly 90% of influenza A cases nationwide. First identified in the U.S. in August 2025, subclade K emerged after the World Health Organization had already locked in this season’s vaccine formula—creating a mismatch between the vaccine and the dominant circulating strain.
Dr. Steven Valassis, chair of emergency medicine at St. Vincent’s Medical Center in Bridgeport, described the situation bluntly: “The rise in flu cases this year is significantly worse than last year and has started earlier than in years past. This trend is unmistakable in our department and throughout the state.”
The data suggests subclade K is more transmissible than previous strains. In Australia, where flu season runs opposite to ours, subclade K extended the season beyond its typical duration.
What the Wastewater Shows
Wastewater surveillance—an early warning system that detects viral presence before symptoms drive people to seek care—paints an even grimmer picture. Every CDC testing site in Connecticut except Litchfield is showing “very high” flu activity. The Northeast region leads the nation in flu spread.
Dr. Scott Roberts, head of infection prevention at Yale New Haven Hospital, explained why this matters: “Hospitalizations always lag behind wastewater and test positivity, because most people are not sick enough to go to the hospital when they start having symptoms or get infected. I would certainly expect hospitalizations to follow wastewater, which means we’re likely going to see increases in the coming weeks.”
Roberts said Yale New Haven is “already quite full” and warned that “health care systems need to be prepared for a coming flu wave, worse than it already is.”
The National Picture
Connecticut is part of a broader surge. The CDC estimates 7.5 million flu illnesses, 81,000 hospitalizations, and 3,100 deaths nationwide this season through December 20. The weekly hospitalization rate of 6.2 per 100,000 is the third-highest for this point in the season since 2010.
Neighboring Massachusetts reported 30 flu deaths as of December 21, with 9% of hospitalizations involving influenza—on track to exceed last season’s peak. Only 34% of Massachusetts residents have been vaccinated, down from 38.5% last year.
Should You Still Get the Vaccine?
Yes. Despite the mismatch, the vaccine still works.
Early data from the UK shows the current vaccine is 72-75% effective against severe illness in children and 32-39% effective in adults—within the typical range for H3N2 seasons. European data shows 52-57% effectiveness across age groups.
“Although the flu vaccine is not a perfect match for this year’s dominant flu strain, it still offers meaningful protection especially in decreasing severe illness, hospitalization and death,” Valassis said.
Commissioner Juthani noted one bright spot: Connecticut has seen “a small increase over last year in the number of people getting their flu shots.”
What to Do Now
If you haven’t been vaccinated, it’s not too late. The season hasn’t peaked.
If you get sick, antivirals like Tamiflu remain effective against subclade K—the mutations that help it evade vaccine antibodies don’t affect antiviral drugs. But antivirals work best when started within 48 hours of symptom onset.
Beyond that, the standard advice applies: wash hands frequently, cover coughs and sneezes, and stay home when sick.
Dr. Roberts summed up the outlook: “We’re still going up, and we don’t have an end in sight. So until we start to see this slope start leveling off, I think we just got to be prepared for more flu in the next few weeks.”
Sources
- CT Insider - Connecticut’s flu season is bad and getting worse, with ’no end in sight,’ doctors say
- CDC - Weekly US Influenza Surveillance Report: Week 51
- CDC - Preliminary Estimated Flu Disease Burden 2025-2026
- CIDRAP - With an absent CDC and mismatched ‘subclade K’ flu strain, experts face upcoming season with uncertainty
- GAVI - “Superflu” or same old flu? How subclade K influenza is playing out worldwide
- WAMC - As flu cases surge in Massachusetts, health professionals urge vaccination
- Eurosurveillance - Early influenza virus characterisation and vaccine effectiveness in England