New H3N2 Subclade K Influenza Variant Spreads in the U.S.

A new variant of the influenza A(H3N2) virus, known as subclade K, is spreading across the United States, contributing to a rise in flu cases and hospitalizations. The Centers for Disease Control and Prevention (CDC) reports that influenza A(H3N2) viruses are currently the most frequently reported influenza viruses this season, with subclade K accounting for 89% of these cases.

The Pan American Health Organization (PAHO) has noted a progressive increase in detections of subclade K in North America, particularly in the United States and Canada. While no significant changes in clinical severity have been observed, seasons dominated by the A(H3N2) subtype have historically been associated with greater impact among older adults.

The current flu vaccine was formulated before the emergence of subclade K, leading to concerns about its effectiveness against this new variant. However, preliminary data from Europe indicate that vaccination continues to provide protection comparable to previous years against severe disease, including hospitalization. The CDC emphasizes that vaccination remains the best defense against severe illness from influenza.

Health authorities recommend that individuals, especially older adults and those with risk factors, receive the flu vaccine to reduce the risk of severe illness. Additional preventive measures include regular handwashing, covering coughs and sneezes, and staying home when experiencing fever or respiratory symptoms.