If you think back to COVID days, virus mutations are nothing new. This year, health experts are flagging a variant of the seasonal influenza virus that might not be well matched to this year’s flu shot. Connecticut Children’s Ian Michelow, MD, infectious diseases specialist, walks through the facts, what we know, what we don’t yet know, and concrete steps families can take to protect children, themselves and loved ones.
What’s new with the flu this year?
A version of influenza A subtype H3N2 — the “subclade K” — has been identified spreading in parts of the Northern Hemisphere.
This particular variant is less well matched to the vaccine composition for the 2025-26 influenza season even though the flu shot is designed to protect against influenza A H3N2 viruses.
Some regions (for example the U.K. and Japan) have reported an earlier-than-usual start to the flu season and a higher proportion of H3N2 cases compared with other circulating influenza strains. Fortunately, it doesn't appear to be causing more severe disease.
According to the Centers for Disease Control and Prevention (CDC), the 2024-25 U.S. flu season was one of the most severe in many years — influenza A was the culprit, and the peak positivity (roughly 30 %) was the highest in the past nine seasons.
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It is important to remain vigilant but not time to panic.
Reasons to be vigilant about subclade K:
Because children may not be protected from infections during prior seasons and the current flu vaccine may not provide optimal protection, we may see more cases than in a “typical” flu season this year.
In general, H3N2 strains can cause more severe illness (especially among older adults, young children, and immunocompromised people) compared with some other influenza subtypes.
An earlier season start can mean more people become infected over the entire winter season.
Why it’s not time to panic:
The current flu shot may still reduce severity of illness even if it doesn’t entirely prevent infection.
Even with mismatches in past seasons, vaccination has helped reduce hospitalizations and severe outcomes, such as ICU admission and death.
We’re still getting updated surveillance data, so it’s wise to stay alert — but we don’t truly know what the full impact on the U.S. will be just yet.
Bottom line: It’s wise to be more vigilant this year — but we aren’t at a crisis stage. The key is to use every tool we have (vaccines, hygiene, early treatment) to keep our kids, families and communities safe.
If you catch the flu, symptoms will likely be less severe if you are vaccinated. Immunization against flu is still one of the best safeguards against severe complications.
Ian Michelow, MD, Pediatric Infectious Diseases Specialist,
Connecticut Children's
Should my child still get their flu shot?
Absolutely. If there’s ever a year to get a flu shot, this is it.
There are also a few other strains of the flu, all of which the flu shot protects against, such as influenza H1N1 and B subtypes. If you catch the flu, symptoms will likely be less severe if you are vaccinated. Immunization against flu is still one of the best safeguards against severe complications.
Make sure children who are eligible (including those as young as 6 months old, preschool and school-aged kids, and those with chronic health issues) get their annual flu shot.
What else can help protect against infection this flu season?
A lot. For starters, encourage a healthy immune system. Good nutrition, adequate sleep, and managing chronic conditions all matter.
Also:
Keep up regular well-child visits, including any recommended vaccinations and check-ups.
Model basic respiratory hygiene and hand hygiene—teach children to wash hands well (20 seconds, soap and water) or use hand sanitizer after being out, before eating, after coughing/sneezing.
Encourage covering coughs and sneezes (into the elbow or a tissue) and disposing of tissues promptly.
If your child is sick (fever, cough, sore throat), keep them home to reduce spread.
Avoid crowded indoor spaces when flu is on the rise, and open windows to ventilate the home whenever possible.
Interrupting social activities isn’t realistic for anyone, but consider cutting down on time spent in very crowded, poorly ventilated indoor places. Wearing face masks in crowded spaces can help reduce the risk of getting sick.
When can flu become an emergency in kids?
Stay alert for signs that need urgent medical attention: difficulty breathing, bluish lips/face, persistent high fever, worsening instead of improving.
Monitor updates from local health departments (e.g., for Hartford and Fairfield Counties, CT), school notifications, and your child’s school or childcare center. When the flu season is high in your area, be extra vigilant. Wash your hands properly, wear a mask, keep your distance—you know the drill from the COVID days.
