A mutation of the influenza A virus, known as the H3N2 K subclade, has led to increased hospitalizations in Europe and the United States, though no more severe cases are reported. In Latin America, including Mexico, preventive surveillance is in place without this variant predominating. Authorities recommend vaccination for vulnerable groups amid the risk of spread.
The H3N2 variant of influenza A, first identified in US pigs in 2010, has mutated into a K subclade (J.2.4.1) showing antigenic drift from the 2025-2026 seasonal vaccine. Over 80% of analyzed H3N2 viruses belong to this subclade, triggering alerts in Europe and the United States, per the Centers for Disease Control and Prevention (CDC).
In the United Kingdom, the first week of December saw 1,700 flu hospitalizations, a 63% increase from the previous week. In the US, 905 confirmed influenza hospitalizations are reported at the season's start, with 73.5% due to H3N2, mainly affecting those over 65 at a rate of 7.5 per 100,000. The World Health Organization (WHO) notes peaks in Germany, France, Italy, Spain, Canada, and Japan. There is no evidence of greater severity than other subtypes.
In Latin America, influenza A is rising, but H3N2 does not predominate. Argentina reports 7,549 cases in 2025, with only 17 H3N2 and 218 total influenza deaths. Brazil detects isolated cases, such as 20 in Santa Catarina. Mexico has 402 confirmed cases, mostly H1N1, without specific H3N2 counts.
Mexico City's Health Secretariat, led by Nadine Gasman, maintains preventive alerts with surveillance at the International Airport and bus terminals to detect symptoms in travelers. Gasman stressed: 'Mexico has tetravalent vaccines that offer protection against the H3N2 subtype' and urged vaccination for children aged 6 months to 5 years, pregnant women, seniors, and those with comorbidities.
Symptoms include fever over 39°C, cough, sore throat, extreme fatigue, and nasal congestion. Prevention focuses on vaccination, hand hygiene, and healthy lifestyles. The coming weeks will be crucial to assess risks in Latin America.
