A new variant of the influenza A(H3N2) virus, scientifically designated as subclade K (or J.2.4.1), is causing widespread concern globally, although it is colloquially referred to as the "Super-K" or "super flu." This strain was initially identified by the CDC in August 2025 and rapidly expanded after being noted in the Southern Hemisphere, including Australia and New Zealand. It has become the predominant influenza A strain circulating in the current 2025-2026 Northern Hemisphere flu season. While the World Health Organization (WHO) indicates that overall global influenza activity remains within expected seasonal ranges, some regions have experienced early and higher-than-typical activity. For instance, the United States is facing a significant flu season, with CDC estimates of at least 15 million illnesses, 180,000 hospitalizations, and 7,400 deaths so far. Reports suggest some states, like Michigan and Tennessee, are seeing record hospitalizations, leading to characterizations of it being the worst flu season in a quarter-century for those areas. Japan and the UK have also reported early and intense flu activity linked to this strain. Experts note that the H3N2 subclade K has undergone several mutations, differing from the strains used to formulate the 2025-2026 flu vaccines. This raises questions about vaccine effectiveness, though early data from the UK suggests the current vaccine still offers meaningful protection, particularly against severe illness and hospitalization (72-75% in children, 32-39% in adults). The WHO emphasizes that current epidemiological data do not indicate increased disease severity associated with subclade K, with its clinical presentation being similar to other seasonal influenza. Public health bodies globally are recommending vaccination and continued surveillance to monitor the strain's evolution and impact.