The flu season in the Northern Hemisphere is progressing with unusual behavior. Several countries in Europe and the United States are experiencing an accelerated increase in infections caused by the K subclass of the H3N2 virus, a variant that was several weeks ahead of the seasonal calendar and led to sustained increases in doctor visits and hospitalizations. The combination of higher transmissibility, the simultaneous spread of other respiratory viruses and winter population movement puts extraordinary pressure on health systems, according to reports from international organizations.
According to the World Health Organization, flu activity began three to six weeks earlier than expected. In Spain, current figures are well above those of last year and a similar trend can be observed in Germany, France, Italy, the United Kingdom, the United States, Canada and Japan. In all of these countries, the K subclass became predominant, and its advance suggests that the season may even extend into the spring.
Added to this dynamic is the simultaneous spread of the respiratory syncytial virus and SARS-CoV-2, a coincidence that complicates differential diagnoses and increases demand in pediatric wards, long-term care homes and clinics for the elderly.
The H3N2-K subtype has changes on its viral surface that partially reduce the immune system’s ability to recognize it. This characteristic favors transmission in closed and poorly ventilated spaces during the cold months. The most affected groups are children under 5, older adults and people with chronic illnesses.
In this regard, Argentine specialists believe that the situation in the Northern Hemisphere may repeat itself in the next local winter. Enrique Casanueva Martínez, infectious disease specialist and consultant to the Pediatric Infectious Diseases Service at Hospital Austral, explains: “A subgroup is a subgroup, a genetic variant within a larger group, and it is probably what will be circulating in Argentina this winter.”
He also warns that admission could be brought forward: “It may be that some cases arrive earlier due to travel and we need to be vigilant.” As described, the most vulnerable groups will be those already experiencing the greatest impact in the north. “The youngest children, the elderly and people with chronic illnesses that are typical of the flu will be the most affected,” he explains.
Casanueva also emphasizes the need to maintain an updated vaccination schedule: “We must be well vaccinated and get vaccinated again next year and see if we need to adjust the formulas of flu vaccines for next year.”
From a clinical perspective, Ramiro Heredia, doctor at the José de San Martín Hospital de Clínicas, sheds light on the seasonal pattern of the virus in the region. “The flu virus is a respiratory virus that, although it circulates year-round, has a clear pre-seasonal component, with epidemics generally occurring in winter in our region,” he says. He also explains that the Northern Hemisphere experience usually foreshadows what will happen in the South in the following months: “The variants of the flu virus that circulate in the Northern Hemisphere when it is winter there are usually what will reach us in the next flu season in our country.”
Heredia emphasizes that it will be crucial to assess the impact: “We would need to determine the impact this may have on infections and hospitalizations in both general care and intensive care to determine the severity of the disease.”
The current situation has already forced several countries to implement strengthened strategies. Germany, France, Italy, Spain, Canada and the United States have reorganized campuses and care facilities and reintroduced the use of masks in hospitals and health centers. Japan and the United Kingdom have issued specific recommendations for long-term care homes and families with young children, two settings where the virus often spreads quickly.
Vaccination is still the most important way to protect the population. Although protection against this subclass may be lower, vaccination remains the most effective tool for preventing serious disease and reducing hospitalizations, especially in the elderly, patients with chronic diseases, pregnant women, healthcare professionals and children with risk factors. Ventilation of environments, use of masks in enclosed and crowded spaces, frequent handwashing and early consultation in case of symptoms remain essential measures to reduce transmission.
Regarding the vaccination strategy, epidemiologist Hugo Pizzi claims that the H3N2 virus is not unknown, but that this variant shows more aggressive behavior. “H3N2 is one of the most common flu symptoms. A more aggressive variant emerged, the so-called K variant,” he explains.
As outlined above, there has been a significant increase in patients with serious illnesses in the UK. “Given the possible impact they had with around 150 people in intensive care, the English started vaccinating because they were all unvaccinated,” says Pizzi.
Pizzi makes it clear that the situation in Argentina could be better managed if we acted in advance. “Here we have no problems because this arrival will be accompanied by a cold, so the big recommendation today would be to get vaccinated in March.” He believes that early vaccination would have positive effects: “A vaccination in March will put us in a state of incredible stability and is an epidemiological strategy at the highest level,” emphasizes the epidemiologist.
The focus of flu treatment remains on rest, hydration, fever control and medical advice for warning signs. Antibiotics have no effect on the virus and their inappropriate use worsens the global problem of bacterial resistance. In a scenario where multiple respiratory infections coincide, experts recommend avoiding self-medication and seeking professional advice if persistent symptoms or difficulty breathing occur.
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