The WHO (World Health Organization) has issued an alert concerning the increase in the circulation of the influenza virus around the world since October. The majority of cases involve influenza A (H3N2) subclade K (J.2.4.1), a variant called “flu K”.
According to the organization, this growth coincides with the start of winter in the northern hemisphere and the increase in acute respiratory infections caused by viruses typical of the season.
Due to this increase, the seasonal flu season could arrive earlier in the southern hemisphere and therefore in Brazil in 2026, according to an alert issued by PAHO (Pan American Health Organization). Peak circulation of the virus generally occurs here between June and August.
The WHO states that, compared to other circulating strains, current epidemiological data do not indicate an increase in disease severity, although the subtype represents an evolution of influenza A viruses.
In any case, seasons dominated by subtype A (H3N2) are generally associated with greater severity, especially among older people.
Main symptoms
The main symptoms of influenza K are the same as those of a common flu:
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High fever (above 38°C)
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Chills
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Headache
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Muscle and joint pain
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Severe fatigue and prostration
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Dry cough
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Sore throat
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Runny or stuffy nose
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General malaise
According to the Ministry of Health, the situation may vary depending on age.
Children: The body temperature can become very high and it is possible to find “bumps” in the neck (lymph nodes); the patient may also have lung problems, such as bronchitis or bronchiolitis, as well as gastrointestinal symptoms.
Age: It almost always manifests itself as fever, sometimes without other symptoms; Typically, the temperature does not reach such high levels.
Vaccination
The WHO emphasizes that vaccination remains essential to prevent the most severe symptoms of influenza, especially for groups at risk.
At the beginning of December, Anvisa (National Health Surveillance Agency) defined which strains should be included in influenza vaccines in Brazil in 2026, and subtype A (H3N2) is included.
In the SUS (Unified Health System), the flu vaccine is given to the most vulnerable groups. These generally concern children aged 6 months to less than 6 years, pregnant women and the elderly.
Health workers, postpartum women, primary and higher education teachers, indigenous peoples, the homeless and people with chronic illnesses or permanent disabilities can also be vaccinated for free.
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