New Flu Variant Linked to Surge in Severe Cases: Experts Urge Vigilance and Testing

A new influenza variant, identified as subclade K of the H3N2 strain, is causing a significant rise in flu cases and severe illness in several countries, including the United States. Health experts report that this mutated form is spreading rapidly and contributing to an increase in hospitalizations.

Andrew Pekosz, a molecular microbiology professor at Johns Hopkins Bloomberg School of Public Health, confirmed the widespread presence of subclade K in U.S. influenza cases. He noted that “right now we’re seeing clade K everywhere we are seeing influenza,” indicating its dominance in current flu infections.

This variant’s mutations raise concerns about the effectiveness of this season’s flu vaccine. Pekosz explained that while the vaccine might not fully prevent infection by subclade K, it should still reduce the severity of disease and the risk of death. “The mutations may allow it to evade some but not all of the influenza-vaccine-induced protection,” he added.

Current data from the U.S. Centers for Disease Control and Prevention show flu infections increasing, with 89 percent of samples since late September belonging to subclade K. Hospitalization rates nationally remain similar to past seasons but have risen in states like Texas, particularly among seniors aged 65 and older.

Physician Robert Hopkins emphasized the unpredictability of influenza. He said that although the subclade K variant emerged after the vaccine’s development, the flu shot continues to provide important protection, even in this severe flu season. The 2024–2025 flu season was notably severe, and back-to-back difficult seasons are uncommon but possible.

Public health officials urge people to get vaccinated promptly. Pekosz reminded the public, “It is not too late to get a flu shot,” underscoring the vaccine’s role in mitigating disease impact amid evolving flu viruses.

Key Points on Subclade K Flu Variant:

1. Subclade K is a mutated H3N2 influenza A strain driving increased infections globally.
2. The variant may reduce but not eliminate vaccine effectiveness.
3. Flu cases and hospitalizations are rising in many U.S. states – seniors most affected.
4. Ongoing surveillance is critical to monitor severity and spread trends.
5. Vaccination remains a primary defense to reduce severe illness and deaths.

As flu viruses constantly evolve through antigenic drift, experts continue to analyze subclade K’s impact to inform vaccine updates and public health strategies. The flu season usually peaks in February, so monitoring developments remains essential for healthcare preparedness.