Subclade K, a variant of the H3N2 influenza virus, has led to a surge in flu cases in the United States, which are now reaching typical December levels. Experts warn of a potentially complicated flu season, similar to what has been observed in other countries.

Japan, for its part, has already declared a flu epidemic due to subclade K, while the flu season in the UK began a month earlier than usual. This early-start trend is also being replicated in North America.

Cameron Wolfe, professor of medicine and infectious disease specialist at Duke University, points out that subclade K may have bypassed some of the previously accumulated immunity, which could result in a higher number of hospitalizations from the start of the season.

“We are here in mid-November seeing the beginning of a surge that actually mirrors what we have seen overseas,” Wolfe told The Hill.

Subclade K strain

Subclade K refers to a variant of the H3N2 influenza A virus strain that has been dominant in recent flu seasons. It has spread rapidly and raised concerns due to its association with more severe flu symptoms, such as high fever, exhaustion, and intense body aches, compared to milder flu strains like H1N1. It was first detected late in the Southern Hemisphere flu season and is now prevalent in countries such as the UK, Japan, and Canada, and is also present in North America. It is causing the flu season to start earlier and dominate cases in affected regions. Experts warn that this subclade could lead to a severe flu season, especially as it has shown significant genetic divergence from the current Northern Hemisphere flu vaccine strain, which could affect vaccine efficacy. Despite the arrival of a new strain,Flu vaccination rates have declined, especially among children. This is raising concerns among public health experts about the risk of severe outbreaks. Growing skepticism toward public health recommendations, exacerbated by influential figures, has contributed to vaccine hesitancy, according to Dr. William Schaffner of Vanderbilt University. Effectiveness of the current vaccine: Despite concerns about subclade K, initial reports from the UK indicate that this year's flu vaccine still offers some protection. Jarbas Barbosa, of the Pan American Health Organization (PAHO), confirms the expected effectiveness of the current vaccine against the circulating virus. “We expect the current vaccine to remain effective and maintain its effectiveness against the virus that circulates each year,” Barbosa told The Hill. Risk groups: There are risk groups that should receive special attention during the 2025-2026 flu season. These groups include:

It is recommended that these groups receive special attention, including influenza vaccination, to reduce the risk of serious complications from influenza infection.

You may also be interested in: