New Flu Variant May Mean US is in for a Severe Flu Season

Researchers said the 2025–2026 flu vaccine is not an ideal match for the unexpected strain of the influenza A/H3N2 virus, called subclade K, that has been the cause of increasing infection rates in Canada, England, and Japan. Researchers believe this variant will likely drive up cases in the United States as well, and, coupled with lagging vaccination rates, may mean the U.S. is in for a severe flu season.

The subclade K variant evolved further during the southern hemisphere’s 2025 winter flu season. The virus that arose “is projected to predominate during the northern hemisphere’s 2025–2026 influenza season,” the Canadian researchers said in the Journal of the Association of Medical Microbiology and Infectious Disease Canada.

Currently, flu activity in the U.S. is low but rising quickly, primarily among children, according to the latest Centers for Disease Control (CDC) report. The timing of the increasing activity is similar to several past seasons, including the 2024-2025 season.

The CDC recommends that everyone ages 6 months and older get an annual flu vaccine anytime viruses are circulating. More than 121 million doses of flu vaccine have been distributed in the US this season, the CDC reported.

Early analysis finds that this season’s flu shots provide some protection against being hospitalized with this variant, especially for kids. However, data shows many Americans appear to be skipping their flu vaccines this year. This season also follows a severe flu season last winter, during which the U.S. had its highest rates of flu hospitalizations in nearly 15 years, the CDC reported. At least 280 children died of influenza, the highest number since 2004.