New Flu Mutation Causes Severe Illness: See Latest Connecticut Data

CONNECTICUT — Close gatherings over the Thanksgiving holiday could cause an uptick in emergency room visits in Connecticut due to a trio of respiratory illnesses that typically rise this time of year, as well as a new mutation of the common flu that doesn’t respond to this year’s flu shot.

Connecticut emergency rooms typically see an increase in COVID-19, influenza and RSV rates during the holidays. This year’s flu season could be more serious due to a new Influenza H3N2 mutation known as “subclade K,” which is spreading in North America, including the United States.

Although the current flu vaccine offers protection against the H3N2 strain, it doesn’t cover subclade K, which hadn’t been identified when the vaccine was developed. The variant has mutated seven times, making H3N2 an even more serious threat, according to experts.

“Knowing that there’s a new mutated strain out there and H3N2 generally causes more severe disease is concerning,” Dr. Robert Hopkins Jr., medical director of the National Foundation for Infectious Diseases, told NBC’s “Today” show.

The symptoms of the new strain are similar to those caused by common influenza, including fever, chills, body aches, headaches, extreme fatigue, congestion or runny nose, and coughing.

The symptoms come on suddenly. “It’s that hit-by-a-truck feeling,” Hopkins told “Today.”

This particular mutation is now dominant in many countries, including Japan, the United Kingdom and Canada, Forbes reported.

The CDC currently lists Influenza A H3N2 as the cause of most flu cases in the United States. The extent of the spread of the subclade K mutation in the United States is because the Centers for Disease Control and Prevention didn’t do any tracking for its FluView report during the recent government shutdown.

The latest data from the CDC, last updated on Nov. 19, shows that acute respiratory illness rates overall are low in Connecticut.

The Connecticut Department of Public Health confirmed the first death from influenza virus this 2025-26 season was an adult Hartford County resident, 80-89-years-old. This death occurred the week of Oct. 25.

“This is a tragic reminder that the 2025-26 respiratory viral disease season is here. As we approach Thanksgiving and the holidays, more people gather together and spend more time indoors. If you haven’t gotten your seasonal shots, it’s not too late to protect yourself from potential serious complications and protect our most vulnerable,” said DPH Commissioner Manisha Juthani, MD.

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Nationwide, acute respiratory illnesses remain at low or very low levels, according to the CDC; however, emergency room visits for RSV are increasing in many states in the South and Southeast. COVID-19 activity remains low, and seasonal flu activity is low nationally but increasing, according to the surveillance report.

Wastewater surveillance reports from 14 monitoring sites will provide a clearer picture of COVID, flu and RSV rates in Connecticut when the data is updated Friday.

On Sept. 25, it showed low levels of COVID, flu and RSV.