17/11/2025
Key aspects of H3N2 subclade K
Strain: The strain is an influenza A virus, subtype H3N2.
Subclade: It is a new variant, officially named subclade K.
Origin: It emerged at the end of the southern hemisphere's 2025 season.
Vaccine mismatch: This subclade did not match the vaccine strain chosen by the WHO for the upcoming season, which is a concern for vaccine effectiveness.
Dominance: Early data from Japan and the UK shows it represents a high percentage of flu samples (up to 90%).