Several schools in the United Kingdom have had to temporarily close their doors in recent days due to an unusual surge of seasonal flu, caused by a mutation of the H3N2 subvariant known as 'subclade K'. The most significant outbreak occurred in Caerphilly (Wales), where more than 250 students and staff fell ill simultaneously. Consequently, educational authorities opted for a thorough disinfection and a temporary suspension of classes to mitigate the spread of infections. Symptoms among affected students (vomiting, fever, diarrhea, headache, and fatigue), similar to those of COVID-19, forced several centers to suspend their activities. Additionally, chills often appear very abruptly with this strain. According to Noticias Argentinas, the decision comes at a time of increasing pressure on the National Health Service (NHS), which recorded 1,717 flu hospitalizations by the end of November—the highest figure for this period in recent years. Meanwhile, the UK Health Security Agency (UKHSA) has warned that the mutation has increased the virus's transmissibility, although the vaccine's efficacy remains stable compared to previous seasons. As this new H3N2 flu subclade K variant is highly transmissible, experts predict a sharp increase in cases and have warned of the risk of co-infections (flu and avian flu) and advised urgent vaccination. The high transmissibility of this variant is attributed to significant genetic changes within the subclade K, according to experts.