Epidemiological Alert: Seasonal Influenza and Other Respiratory Viruses —Start of the Southern Hemisphere Season— 27 April 2026

With the start of the 2026 season of respiratory virus circulation in the Southern Hemisphere, and considering the experience of the 2025–2026 season in the Northern Hemisphere—characterized by the predominance of influenza A(H3N2) virus of the K subclade, with evidence of intense activity concentrated in a short period and moderate effectiveness of the influenza vaccine—the Pan American Health Organization / World Health Organization (PAHO/WHO) urges Member States to strengthen integrated epidemiological and virological surveillance of respiratory viruses, including timely genomic characterization; adjust health service preparedness and organizational plans in anticipation of possible concentrated increases in demand for services due to the circulation of influenza A(H3N2) and the potential co-circulation of respiratory syncytial virus (RSV); and accelerate vaccination against seasonal influenza and RSV in priority groups before the peak of circulation.