NATIONWIDE – The United States may be heading into a second severe flu season in a row, driven by a new, mutated strain, subclade K. This variant is already driving early surges in the United Kingdom, Canada, and Japan, raising concerns among infectious disease experts.
Last winter was already extreme, with the U.S. recording its highest rates of flu hospitalizations in nearly 15 years and at least 280 pediatric deaths, the highest number since reporting began in 2004. With a new variant emerging and holiday travel approaching, experts fear the situation could worsen in the coming weeks.
A New Variant Emerges
Flu activity in the U.S. is currently low but is rising quickly, according to the latest FluView report from the U.S. Centers for Disease Control and Prevention (CDC).
- Dominant Strain: Most viruses identified this season are the H3N2 A strain.
- Subclade K: Half of those H3N2 viruses belong to subclade K, a variant responsible for a rougher-than-normal flu season this summer in the Southern Hemisphere.
- Vaccine Mismatch: Subclade K was not a major player when scientists determined the composition of the annual flu shots, meaning the current vaccines cover a related but slightly different group of viruses.
“It’s not like we’re expecting to get complete loss of protection for the vaccine, but perhaps we might expect a little bit of a drop-off if this is the virus that sort of dominates the season,” said Dr. Richard Webby, director of the WHO Collaborating Center at St. Jude Children’s Research Hospital.
Despite the mutations, scientists found that the current flu vaccines are still offering decent protection against subclade K viruses:
- Children: Vaccination cuts the odds of an emergency department visit or hospitalization by almost 75%.
- Adults: Effectiveness for adults, including those over 65, was lower, around 30% to 40% against needing a hospital or ER visit.
These results are from a recent preprint study and are considered early data, but experts stress that some protection is far better than none.
Compounding the variant concern is a drop in flu vaccination rates across the U.S.
- Fewer Shots: New data from IQVIA shows that vaccinations are down compared to this point last year. Retail pharmacies administered about 26.5 million flu shots between August and the end of October, which is more than 2 million fewer than the 28.7 million given during the same period in 2024.
- Global Precedent: Flu vaccinations also fell in Australia, where subclade K was the predominant virus, leading to a record season with more than 443,000 cases.
Dr. Jennifer Nuzzo, who directs the Pandemic Center at Brown University’s School of Public Health, noted that vaccine skepticism has “injected chaos into the whole vaccination system,” leaving many people confused or worried about getting vaccinated.
Lab testing and wastewater surveillance are both indicating a rapidly increasing presence of the flu.
- Lab Tests: Data from diagnostic companies show the percentage of tests positive for type A flu has risen sharply, aligning with CDC trends.
- Wastewater: In October, 18% of samples in the WastewaterSCAN network were positive for type A flu; that number rose to 40% in November.
As the rise in cases observed in the UK and Japan serves as a potential “bellwether” for North America, experts are urging the public to get vaccinated immediately.
“I am concerned… that we could have a big flu season this year based on what we’re seeing in other parts of the world,” said Dr. Adam Lauring of the University of Michigan Medical School. “It’s not too late. Go and get your flu shot.”
