Flu Season Hits Hard as H3N2 "Super Flu" Sweeps Across the U.S.

Much like a winter storm system that meteorologists track as it intensifies and moves across the country, this year's influenza season is following a similar pattern: building strength, spreading rapidly, and leaving communities struggling to prepare for its impact.

The 2025-2026 flu season has proven to be one of the most severe in recent years, with a particularly aggressive strain of Influenza A known as H3N2 subclade K dominating cases nationwide. According to the CDC's most recent data for the week ending January 3, the hospitalization rate for long-term care residents with positive flu tests reached 54.1 per 100,000, reflecting significant increases across most regions.

A Perfect Storm of Factors

The severity of this season stems from multiple converging factors. The H3N2 subclade K strain, which accounts for approximately 90% of characterized H3N2 viruses this season, has proven especially challenging. This variant emerged after vaccine compositions were finalized in February 2025, leading experts to call it an "antigenic drift." This means the circulating virus has mutated enough to reduce vaccine effectiveness somewhat.