In mid-December, Google searches for the “super flu” caused by the H3N2 virus peaked in attention in Mexico, driven by a spiral of fake news warnings of a “new pandemic.” Although it is old knowledge – and not the emergence of a new infectious agent as happened with the new coronavirus – the H3N2 virus has become famous in recent weeks for having incorporated a series of mutations that have caused an increase in its circulation, prolonging the flu season in the southern hemisphere and advancing it in regions of the northern hemisphere such as the European Union and Japan. However, the global panorama has nothing to do with the pandemic scenario that put health systems under control at the start of 2020.
What is H3N2 flu?
It is one of the viruses responsible for seasonal influenza, which, year after year, causes an increase in respiratory illnesses that coincides with the arrival of autumn and winter. Along with the H1N1 flu, the H3N2 virus is one of the most circulating viruses during the season which, in Mexico, generally lasts from October to May. “Influenza viruses have a biological characteristic that causes them to undergo mutations and changes. From time to time these accumulate and produce more changes and generate different characteristics from the others. Every year there is one influenza virus that predominates and what happens is that different epidemiological surveillance systems in several countries have warned that the predominant virus is an AH3N2 type virus and all the surveillance protocols say that it must continue to be studied,” said Mauricio Rodríguez Álvarez, spokesperson for the risk program, explains to this newspaper. UNAM epidemiological studies.
On December 12, the Pan American Health Organization (PAHO) called on member countries to promote vaccination with a focus on the elderly and to strengthen surveillance of the virus in the region, given its recent circulation in Europe, Asia, the United States and Canada: “Health authorities in these countries have not reported significant changes in clinical severity, but historically, seasons dominated by the A(H3N2) virus are generally associated with a greater impact on the elderly”, explains the OPS in a press release.
This is not a pandemic threat
Rodríguez is categorical when he assures that there is no point of comparison between the effects of the H3N2 flu and the emergence of SARS-CoV-2, which caused the covid-19 pandemic that began in March 2020. “We are not facing a virus that leaves us without protection like the covid virus. “The H3N2 virus is not a pandemic threat, because we have many elements that help us reduce its impact: the first is the sentinel system, epidemiological surveillance of respiratory viruses; the second, diagnostic tests; the third, clinical suspicion, the knowledge of doctors; the fourth is oseltamivir as a specific antiviral for patients; and the fifth is vaccination for several years against seasonal flu, which generally has a level of protection.”
In light of current data, Rodríguez explains that there is no evidence that H3N2 causes more severe illness or that it affects any age group other than usual. Although the WHO says the flu remains within expected ranges globally, the high circulation of the virus suggests it is slightly more transmissible. “The important thing is that it is a seasonal virus that is monitored and what we need to do is avoid contagion in the community,” he explains. From the UNAM research program on epidemiological risks of which he is part, Rodríguez emphasizes the need to prevent infections with the same prevention measures popularized during the covid-19 pandemic, such as the use of face masks in case of symptoms of respiratory illness and flu vaccination to reduce the risk of serious illness and hospitalization.
Symptoms and treatment
Like other viruses that cause respiratory illnesses, influenza caused by H1N1 or H3N2 manifests itself with fever, cough, sore throat, muscle pain and general fatigue. Rodríguez indicates that even if a test is necessary to know which respiratory illness it is, “in practice, it is the same flu: neither the patient nor the attending physician makes a difference if the virus is H1N1 or H3N2 from before, or H3N2 from the K subclade”, he assures. “It’s the same route of infection, the same incubation period of one or two days; the same clinical manifestation with fever, cough, joint pain, headache; the diagnosis is made with the same type of tests and the same treatment is administered, which is oseltamivir, the specific antiviral against the influenza virus.”
H3N2 in Mexico
In Mexico, according to Ministry of Health data updated as of December 7, 2025, 952 positive cases have been confirmed so far during the seasonal flu season. This is the lowest figure in the last three years for the same epidemiological week, with a prevalence of 71.5% of infections caused by the H1N1 virus and 16.2% by H3N2. On December 12, the head of the Secretariat, David Kershenobich, reported the detection of the country’s first case of influenza caused by the H3N2 subclade K virus in a patient in the capital who responded to outpatient treatment with antiviral drugs and recovered satisfactorily. “The most likely thing is that in Mexico the H3N2 virus will cause the flu wave that we have every year and that it will be the dominant virus, we could expect that,” Rodríguez says. “What we need to do as a society is interrupt the transmission of this virus and all other respiratory viruses in the community, prevent contagion in the community. That’s the key.”
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