Variante K del H3N2 adelanta temporada de influenza más intensa en Chile

Chile is entering an influenza season unlike the ones health officials had prepared for. What looked like a routine autumn and winter has instead become a public health emergency, driven by a specific variant of the flu that first emerged in Ohio in the fall of 2025 and then overwhelmed hospitals across the Northern Hemisphere. That same strain—the K variant of H3N2—is now the dominant force behind a surge in respiratory illness across Chile, according to the Public Health Institute.

The numbers tell the story of acceleration. In the epidemiological week spanning May 17 to 23, respiratory samples came back positive at a rate of 45.2 percent, up from 41.4 percent the week before. Influenza A, driven largely by the H3N2 subtype, now accounts for 27.6 percent of all detected respiratory viruses, making it the second most common. Nearly 29 percent of all emergency room visits in the country are now for respiratory causes. Adult critical care beds are occupied at 92 percent capacity. This is not a projection or a worst-case scenario being modeled in a conference room. The pressure on hospitals is happening now.

What makes this variant different from previous flu seasons is how it behaves in the body and how it spreads. The H3N2 variant K has a particular affinity for healthy, working-age adults—people without chronic illnesses who might assume they are not at risk. It produces sustained high fever lasting three to five days, complete physical exhaustion, and typically keeps people out of work for a week to ten days. More troubling still is that the virus transmits before symptoms appear. A person can feel fine, go about their day, and unknowingly infect others. Children between five and fourteen are where influenza A is circulating most actively right now, and emergency room visits for lower respiratory infections in that age group jumped 9.7 percent in the most recent week. Schools become the vector, carrying the virus home to grandparents and immunocompromised family members.

The vaccination campaign has achieved 68.6 percent coverage nationally, but that aggregate number masks dangerous gaps in the groups most vulnerable to severe illness. People aged 60 and older have reached only 55.7 percent coverage. Children from six months to five years sit at 55.6 percent. Pregnant women are at 57.5 percent. These are the populations for whom influenza carries the highest risk of hospitalization and death. Meanwhile, working-age adults—the ones spreading the virus most efficiently—have lower vaccination rates still. A vaccinated adult reduces the chance of transmitting the virus to family members by up to 70 percent, yet millions remain unprotected.

Dr. Carolina Herrera, a pulmonary specialist, emphasizes that this variant strikes people who do not perceive themselves as vulnerable. "What is concerning is that it hits hard at young, healthy adults, who often do not see themselves at risk," she explains. Prevention measures—ventilation, appropriate clothing for cold weather, annual vaccination—are not one-time interventions but ongoing strategies that reduce virus circulation and protect the entire community. The window to get ahead of this is closing. July is typically when respiratory illness peaks in Chile, and health authorities warn that the most complex surge has not yet arrived.

Dr. Loreto Twele, head of emergency services at Puerto Varas Clinic, notes that emergency rooms are already feeling the pressure. "We are already seeing the strain of this season, and the worst peak has not come yet," she says. Early medical consultation matters because antivirals work best in the first 48 hours of illness, and vaccination requires about 15 days for the body to build protection. The message from specialists is urgent but clear: the time to act is now, before July arrives and the system becomes overwhelmed. Against a virus that does not distinguish between risk groups, the only effective defense is a culture of prevention that protects everyone.