Overview
- U.S. surveillance shows overall flu activity remains relatively low but is rising among children and young adults, and the H3N2 subclade K has now been detected nationally.
- Subclade K accounts for about 90% of recent influenza cases in countries such as the United Kingdom and Japan and is becoming dominant across North America and Europe.
- Scientists report antigenic drift in the variant’s haemagglutinin that differentiates it from the vaccine strain and may lower vaccine effectiveness this season.
- This season’s vaccine could not be updated in time for the drifted strain, yet experts and the CDC still recommend vaccination for protection, particularly for high‑risk groups.
- Health systems in parts of Asia, including multiple provinces in China, report high flu activity with crowded hospitals, especially for pediatric patients.