Flu Season Could Be Brutal This Year. What to Know About a New Strain
A new variant of influenza H3N2 is spreading in other countries. But that could mean the U.S. is in for a rough flu season.
The mutated strain, known as subclade K, is causing a surge in cases in the United Kingdom, Canada, and Japan.
While H1N1 predominated flu season this year in the Southern Hemisphere, with the H3N2 subclade K taking off only at the end, early data from the UK and Japan show H3N2 subclade K was represented in 90% of flu samples, the University of Minnesota wrote in a report earlier this month.
With a new strain spreading and less Americans getting vaccinated, the sick season might be brutal.
Here’s what to know.
Where has the H3N2 subclade K strain been detected?
According to the European Centre for Disease Prevention and Control, the strain has been detected on all continents and accounts for a third of all A (H3N2) sequences deposited in the Global Initiative on Sharing All Influenza Data between May and November 2025 globally, and almost half in the European Union.
Real-world vaccine effectiveness data are currently limited, the report shows. However, vaccines are still expected to provide protection against severe disease.
The risk for an influenza season dominated by H3N2 subclade K is moderate, available information from the agency suggests. The risk is higher for populations at higher risk for severe diseases, including people over the age of 65, people with underlying metabolic, pulmonary, cardiovascular, neuromuscular and other chronic diseases, pregnant people or persons who are immunocompromised.
What impacts could the new flu strain have?
The agency cautions that a larger epidemic driven by lower immunity to infection could result in a higher number of hospitalizations and increased pressure on healthcare services, though it noted the assessment may change as more data becomes available.
It’s difficult to determine how the strain is spreading across the U.S. because critical flu data was not being tracked by the Centers for Disease Control and Prevention during the 43-day government shutdown. However, the latest FluView report shows flu activity is low but rising quickly.
The strain has dominated the start of the 2025 to 2026 influenza season in England, the UK Health Security Agency said in a published pre-printed report earlier this month. The report has not yet been peer reviewed.
The burden has been greatest in children and young adults, the agency said, adding early estimates provide reassurance that vaccines protect against infection in those groups.
What are the latest flu symptoms?
Symptoms associated with H3N2 are similar to all influenza flu viruses and include:
However, the strain could result in higher fevers and complications.
A child receives one of two vaccinations for flu and COVID-19 at the Cumberland County Department of Public Health in Fayetteville, North Carolina.
What to know about the flu vaccine
The CDC recommends those 6 months and older, with rare exceptions, to get vaccinated.
Despite the CDC recommendation, people are seemingly getting the shots less and less. According to CDC data, the doses of flu vaccines distributed has steadily decreased since the 2021-22 flu season.
For the 2024–25 season, 147.6 million doses of flu vaccine were distributed U.S. with March 8, 2025 being the final date updated. The season before showed 157.7 million doses distributed with the final reporting date of March 9, 2024.
Regularly wearing masks in tight indoor spaces and washing hands for at least 20 seconds can help reduce the likelihood of infection.
What happened in last year’s flu season?
Here’s a look at the preliminary estimated flu numbers from last year’s flu season, which spanned from October 2024 to May 2025, according to CDC data.
The numbers are much higher compared to the prior 2023 to 2024 Influenza season, when the CDC saw 27,965 deaths, 470,676 hospitalizations, 18,175,153 medical visits and 40,195,708 flu illnesses.
Contributor: Michelle Del Rey – USA TODAY
While H1N1 predominated flu season this year in the Southern Hemisphere, with the H3N2 subclade K taking off only at the end, early data from the UK and Japan show H3N2 subclade K was represented in 90% of flu samples, the University of Minnesota wrote in a report earlier this month.
With a new strain spreading and less Americans getting vaccinated, the sick season might be brutal.
Here’s what to know.
Where has the H3N2 subclade K strain been detected?
According to the European Centre for Disease Prevention and Control, the strain has been detected on all continents and accounts for a third of all A (H3N2) sequences deposited in the Global Initiative on Sharing All Influenza Data between May and November 2025 globally, and almost half in the European Union.
Real-world vaccine effectiveness data are currently limited, the report shows. However, vaccines are still expected to provide protection against severe disease.
The risk for an influenza season dominated by H3N2 subclade K is moderate, available information from the agency suggests. The risk is higher for populations at higher risk for severe diseases, including people over the age of 65, people with underlying metabolic, pulmonary, cardiovascular, neuromuscular and other chronic diseases, pregnant people or persons who are immunocompromised.
What impacts could the new flu strain have?
The agency cautions that a larger epidemic driven by lower immunity to infection could result in a higher number of hospitalizations and increased pressure on healthcare services, though it noted the assessment may change as more data becomes available.
It’s difficult to determine how the strain is spreading across the U.S. because critical flu data was not being tracked by the Centers for Disease Control and Prevention during the 43-day government shutdown. However, the latest FluView report shows flu activity is low but rising quickly.
The strain has dominated the start of the 2025 to 2026 influenza season in England, the UK Health Security Agency said in a published pre-printed report earlier this month. The report has not yet been peer reviewed.
The burden has been greatest in children and young adults, the agency said, adding early estimates provide reassurance that vaccines protect against infection in those groups.
What are the latest flu symptoms?
Symptoms associated with H3N2 are similar to all influenza flu viruses and include:
- Fever
- Cough
- Runny nose
- Fatigue
- Muscle aches and chills
However, the strain could result in higher fevers and complications.
A child receives one of two vaccinations for flu and COVID-19 at the Cumberland County Department of Public Health in Fayetteville, North Carolina.
What to know about the flu vaccine
The CDC recommends those 6 months and older, with rare exceptions, to get vaccinated.
Despite the CDC recommendation, people are seemingly getting the shots less and less. According to CDC data, the doses of flu vaccines distributed has steadily decreased since the 2021-22 flu season.
For the 2024–25 season, 147.6 million doses of flu vaccine were distributed U.S. with March 8, 2025 being the final date updated. The season before showed 157.7 million doses distributed with the final reporting date of March 9, 2024.
Regularly wearing masks in tight indoor spaces and washing hands for at least 20 seconds can help reduce the likelihood of infection.
What happened in last year’s flu season?
Here’s a look at the preliminary estimated flu numbers from last year’s flu season, which spanned from October 2024 to May 2025, according to CDC data.
- 610,000 to 1.3 million flu hospitalizations
- 27,000 to 130,000 flu deaths
- 47 million to 82 million flu illnesses
- 21 million to 37 million flu medical visits
The numbers are much higher compared to the prior 2023 to 2024 Influenza season, when the CDC saw 27,965 deaths, 470,676 hospitalizations, 18,175,153 medical visits and 40,195,708 flu illnesses.
Contributor: Michelle Del Rey – USA TODAY