What is the “super influenza” that is spreading in Europe and America?

spread of influenza This fall, the severity of the crisis increased, particularly in the United States and the United Kingdom. The U.S. Centers for Disease Control and Prevention specified 2024-25 influenza season as the harshest season From 2017 to 2018. In the UK, the outbreak is starting earlier than at any time since 2003-2004.

Against this background, some media outlet It started using The term “super influenza”. However, this term is not an official medical term. Its actual name is “subclade K” and it is a new variant of influenza A H3N2.

This variant has multiple mutations in a protein called hemagglutinin on the surface of the virus, making it antigenically different from the variants used in existing vaccines. This allows them to partially evade immunity acquired through previous infection or vaccines, making people more susceptible to infection. Genetic analysis by the UK Health and Safety Executive found that revealed Eighty-seven percent of H3N2 viruses detected since late August 2025 are reported to be subclade K.

The epidemic started earlier than usual

The term “super flu” is not always scientifically accurate. The H3N2 strain already causes severe illness in the elderly and children, and the new variant does not make it any more deadly. Despite its name, the inherent danger of the virus is said to be no different from the previous H3N2 strain.

In 2025, the U.S. influenza pandemic peaked in early February, with active outbreaks occurring in 87.3% of the country. Over 50% of the nation for 11 consecutive weeks recorded a high prevalence levelthe abnormality that caused the 287 death of a child. However, these numbers reflect the scale of the epidemic and do not imply an increase in the lethality of the virus itself.

Early this year, many parts of the world experienced an influenza pandemic. In Japan, the peak period in normal years is from late December to February, but in 2025, the epidemic began in earnest from the end of September. According to the Ministry of Health, Labor and Welfare, of the 23 strains of H3 viruses collected in Japan between September and November 5, 22 of the strains that could be analyzed were subclade K.

The reason why the epidemic occurred so early is thought to be due to a decline in the immunity of the public due to measures taken against infectious diseases. Novel coronavirus infection (Covid-19)as well as a decline in physical strength due to record-breaking heat. During the three years of the coronavirus pandemic, influenza epidemics have been largely brought under control. As a result, population immunity against the virus may have declined. In fact, Australia experienced an influenza pandemic in 2024. at the highest level It would be no surprise to see a similar trend in the Northern Hemisphere since 2019.

Existing vaccines are effective

There is also great interest in vaccine efficacy in the face of this virulent strain. The vaccine for the 2025-26 season is based on the conventional J.2 strain (subclade), which is antigenically different from subclade K. However, early data from the UK confirms that 70-75% of vaccinated children and 30-40% of adults did not visit an emergency room or be hospitalized after becoming infected. This means that the vaccine remains effective in preventing severe disease even if the antigenicity is not completely identical.

Basic preventive measures are the same as for traditional influenza. Vaccination is recommended between October and November, before the outbreak, and the vaccine becomes effective approximately two weeks after vaccination. Especially recommended for people over 65 years old, people with underlying health conditions, pregnant women, children between 6 months and 5 years old, and healthcare workers. In daily life, it is effective to thoroughly wash and disinfect your hands and wear a mask when in crowded places. Ventilating the room and maintaining appropriate humidity are also important to suppress virus activity.