H3N2 Variant Drives Flu Cases Up in North America, Europe

Health officials across North America and Europe are alerting the public to a rapidly spreading variant of the influenza A H3N2 virus, known as subclade K, as flu season intensifies in late 2024 and early 2025. Detected in at least 34 countries over the past six months, according to the World Health Organization, this mutated strain has emerged as the dominant form circulating in the United States, Canada, and the United Kingdom, driving up cases and hospitalizations just as holiday travel and gatherings peak.

The Centers for Disease Control and Prevention reports that subclade K accounts for nearly 90 percent of analyzed H3N2 samples in the U.S. since late September. In Canada, Health Canada noted a 20 percent increase in positive flu tests during the first week of December, with 6,799 cases confirmed and 91 outbreaks nationwide. Hospitalizations reached 3.6 per 100,000 people that week, particularly affecting children under 19. In the U.K., the UK Health Security Agency recorded a weekly flu positivity rate of 21 percent in England as of early December, up from 17 percent the prior week, with admissions rising to 10 per 100,000.

This variant arose from natural mutations in the...