MercoPress. South Atlantic News Agency

Superflu makes it to Argentina and Brazil

The primary concern for health officials remains low vaccination uptake

Health authorities across South America are on high alert following the confirmed detection of the Influenza A (H3N2) “K subclade” in Argentina and Brazil. The variant, which has already triggered emergency protocols in Chile and Bolivia, is characterized by genetic mutations that may increase transmissibility, though experts emphasize it does not currently appear to be more lethal than standard flu strains.

In Buenos Aires, the “Dr. Carlos G. Malbrán” National Institute (ANLIS) confirmed Argentina's first three cases using genomic sequencing. Two cases were identified in the province of Santa Cruz among adolescents, while another detection affected a hospitalized child in the Buenos Aires Metropolitan Area (AMBA). All three patients recovered without complications. Federal authorities are now coordinating with all 24 provinces to monitor for shifts in severity or infection patterns.

Meanwhile, the Brazilian Health Ministry has identified four initial cases following an “atypical” semester of viral circulation. In the State of Pará, one “imported” case linked to a traveler returning from Fiji was confirmed by the Oswaldo Cruz Foundation (Fiocruz), while three additional cases in the State of Mato Grosso do Sul were first labeled as “under investigation” until the results came out positive for the K variant from the Adolfo Lutz Institute in São Paulo.

In this scenario, Brazilian health authorities warned that the 2026 flu season may arrive earlier and with greater impact due to this variant. The K subclade is not a new disease but a minor genetic variation of the existing H3N2 virus, it was explained. The clinical picture remains identical to the typical flu (fever, cough, fatigue).

Data from Australia and New Zealand —which recently navigated their flu seasons with this variant— showed no increase in death rates. However, they did report a prolonged flu season lasting longer than average.

Health officials in both Argentina and Brazil stressed that current vaccination programs remained effective at preventing severe illness, hospitalization, and death.

The Pan American Health Organization (PAHO) has prompted intensified surveillance due to rising hospitalizations in the Northern Hemisphere.

Rapid tests can identify the strain early, allowing for the timely administration of antivirals, which remain highly effective against the K subclade, the experts also warned. Individuals —especially children and the elderly— should seek immediate care if they experience shortness of breath, prostration, or persistent high fever.

The primary concern for health officials remains low vaccination uptake, which provides the virus with more opportunities to circulate and mutate within the population.

Bolivian authorities are still awaiting international lab results to confirm if a recent H3N2 death in Santa Cruz de la Sierra was specifically the K variant, while the Ñuble region in Chile remains the focal point of the first confirmed localized case in the country.