Early onset of seasonal influenza and emerging RSV activity: Implications for health systems

[EXTRACT]
21 JANUARY 2026, WASHINGTON, D.C. — Globally, influenza activity has increased rapidly in the Northern Hemisphere since October 2025, with transmission continuing to intensify toward the end of 2025. Several countries have experienced an earlier onset and elevated intensity of the influenza season, driven predominantly by influenza A(H3N2) subclade K (J.2.4.1). In some countries in the Southern Hemisphere, influenza activity peaked within the expected seasonal window but persisted slightly longer than usual, with subsequent rebounds of lower magnitude. In this context, the Pan American Health Organization/World Health Organization (PAHO/WHO) has alerted its Member States to remain attentive and to adjust preparedness and health service planning (1). In the Northern Hemisphere, this increase in influenza circulation has been accompanied by a high incidence of outpatient visits for influenza-like illness and increasing influenza-associated hospitalization rates, particularly among adults aged 65 and older. In the Region of the Americas, influenza percent positivity increased during this period, with several countries reporting elevated circulation, including Canada, the United States, and countries in Central America and the Caribbean. Although influenza-related hospitalization rates remained comparable to previous seasons, some countries reported outpatient visit rates higher than usual (Figure 1). Interim estimates from European Union and the United Kingdom indicate that seasonal influenza vaccines for the 2025–2026 Northern Hemisphere season are providing meaningful protection against influenza-associated illness and hospitalization, with higher effectiveness observed in children and more moderate protection in adults. [...]