A new flu variant is spreading rapidly across the Northern Hemisphere, but vaccination remains the best protection against severe illness, the World Health Organization (WHO) said on Tuesday. According to the UN health agency, influenza and other respiratory viruses are surging earlier than usual this season, marked by the emergence and rapid expansion of a new AH3N2 virus subclade. The variant, called J.2.4.1 or subclade K, was first spotted in August in Australia and New Zealand and has since been detected in over 30 countries.
Dr. Wenqing Zhang, Unit Head for Global Respiratory Threats at WHO’s Department of Epidemic and Pandemic Threats Management, told reporters in Geneva that current data do not show an increase in disease severity, though the genetic shift represents a notable evolution in the virus. Flu viruses are constantly changing their DNA, which is why vaccine composition gets updated regularly based on WHO’s tracking through the Global Influenza Surveillance and Response System, a network of influenza centers in 130 countries and a dozen reference laboratories.
The new variant is not part of the latest vaccines produced for the Northern Hemisphere flu season. Still, early evidence suggests that current seasonal vaccines continue to offer protection against severe disease and reduce the risk of hospitalization. “Vaccination remains our most effective defence, including against drifted strains, particularly for high-risk populations and those taking care of them,” Dr. Zhang said. She pointed to early effectiveness data from the United Kingdom published a few weeks ago, which showed the vaccine is around 75% effective against severe disease and hospitalization in children and around 35% among adults.
WHO estimates that seasonal flu causes around one billion cases annually, including up to five million cases of severe respiratory illness and up to 650,000 deaths each year. Dr. Zhang warned that the upcoming holiday season may bring a further surge in respiratory illnesses and urged countries to encourage vaccination and strengthen health system readiness.
When asked whether the United States will remain part of the global surveillance network after its planned departure from WHO on January 22, 2026, Dr. Zhang said that “from the flu perspective, from the respiratory surveillance and preparedness perspective, certainly we would need all the countries in the world to participate in the surveillance, preparedness and a response for influenza and other respiratory viruses because we don’t know the next pandemic strain, when and where it would emerge.” She added that the time between a new strain emerging and being picked up, characterized, and put into vaccines “would make a lot of difference with regards to the number of lives that could be saved.”
