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The identification in Brazil of a new type of influenza A (H3N2) virus, known as “virus K”, is not yet a cause for concern, says the vice-president of the Brazilian Society of Immunizations (SBIm), Renato Kfouri. According to the expert, the circulation of influenza variants is part of the natural dynamics of the virus and, at this moment, there are not enough elements to predict a greater impact in the next flu season..
The identification in Brazil of a new type of influenza A (H3N2) virus, known as “K virus”/ Photo: Reproduction
Any estimate of the severity, duration or intensity of the next season would be premature.
“We don’t know if this will still be the circulating and predominant variant in the world. The season is starting in the Northern Hemisphere. We don’t even know if it will be the H3N2 season or if another H1N1 will come. This is all still very theoretical,” said Kfouri.
Last week, the World Health Organization issued an informative note in which it draws attention to the rapid increase in the circulation of the K variant of Influenza A in the Northern Hemisphere, especially in Europe, North America and East Asia.
In Europe, influenza activity began earlier than usual. The K variant represented almost half of the cases of infections reported between May and November 2025. No significant change in clinical severity has yet been recorded, in terms of hospital admission, admissions to intensive care or death.
This week, the Ministry of Health published a report on the epidemiological situation in the country and highlighted, for the first time, the identification of a case of the K variant in Brazil, in the state of Pará..
This Wednesday (17), the Oswaldo Cruz Foundation (Fiocruz) brought more details about the registration. The sample with the presence of the new variant was collected in Belém (PA), on November 26, and initially analyzed by the Central Laboratory of the State of Pará (Lacen-PA).
After confirmation of influenza A (H3N2), the material was sent to the Oswaldo Cruz Institute (IOC/Fiocruz), where it underwent genetic sequencing.
The case refers to an adult female patient, foreign, from the Fiji Islands, and was classified as imported. To date, there is no evidence of local transmission associated with the variant in Brazil.
For Kfouri, the detection of new variants is expected.
“Every year we have new influenza. It is in the nature of the virus to mutate and cause annual epidemics. That’s why we need to get vaccinated every year. Vaccines are updated according to what can be predicted of what will circulate in the following season”, he explained.
The expert highlights that, even when there is some genetic distance between the vaccine and the circulating virus, protection remains, especially against severe forms of the disease. “Which sometimes means that the effectiveness of the vaccine is a little greater one year than the other year, but effectiveness is never lost. There is always some prospect or expectation of protection, especially against more serious outcomes of hospitalization and death,” he said.
Fiocruz experts reinforce that vaccination remains the main prevention tool. The composition of the vaccine recommended by the WHO was updated in September, with strains closer to those currently in circulation, including the K subclade.
“The composition of the influenza vaccine recommended by the World Health Organization was updated in September for next year, with strains closer to the clades currently in circulation, including the K subclade,” says Marilda Siqueira, head of the IOC’s Laboratory of Respiratory Viruses, Exanthematics, Enteroviruses and Viral Emergencies.
In addition to vaccination, recommendations include frequent hand hygiene, avoiding close contact in case of respiratory symptoms, wearing a mask and seeking medical attention, especially when experiencing fever.. For health services, the main guideline is to maintain the continuous strengthening of epidemiological, laboratory and genomic surveillance.
