The Pan American Health Organization (PAHO) has urged countries across the Americas to strengthen their health service preparedness as the Northern Hemisphere enters the winter season, which typically sees increased circulation of influenza and other respiratory viruses. PAHO emphasized that a combination of vaccination, surveillance, hospital readiness, timely diagnosis and treatment, and personal preventive measures is essential to reduce disease burden, protect vulnerable populations, and prevent strain on healthcare systems.
Data through the end of November 2025 indicate a global rise in influenza activity, largely driven by influenza A viruses. North America is experiencing a sustained increase, while overall activity remains lower in other parts of the Americas. In the Caribbean and Central America, influenza A(H1N1)pdm09 predominates, whereas Canada and the United States are seeing greater circulation of the A(H3N2) subtype, including the emerging subclade K already detected in Europe and Asia. Though no significant increase in severity has been noted, A(H3N2) seasons typically impact older adults more severely. Preliminary evidence suggests that the current influenza vaccine continues to offer similar protection as in previous seasons, especially against severe cases and hospitalizations.
The Southern Hemisphere concluded its 2025 influenza season with a 29% rise in reported severe acute respiratory infections compared with 2024. Respiratory syncytial virus (RSV) primarily affected infants under six months, while influenza largely affected older adults. Influenza circulation began with A(H1N1)pdm09 and later shifted to A(H3N2), without evidence of increased severity. Subclade K had not been detected in South America by early November. RSV circulated earlier than usual, reaching higher levels than in previous years, while SARS-CoV-2 detection was initially high with the XFG variant predominating later. Vaccine studies in eight Southern Hemisphere countries showed moderate protection against influenza A-related hospitalizations and higher protection against influenza B.
PAHO recommended countries strengthen surveillance for influenza, RSV, and SARS-CoV-2, maintain regular reporting and sample sequencing, and promptly investigate unusual respiratory events under the International Health Regulations. National clinical management guidelines should be reviewed and updated, with early diagnosis and antivirals available for high-risk populations. Health services are advised to prepare for potential increases in hospitalizations due to the simultaneous circulation of multiple respiratory viruses.
Vaccination remains critical, particularly for older adults, people with chronic conditions, pregnant women, young children, and healthcare workers. Vaccination during pregnancy and monoclonal antibodies for newborns significantly reduce severe RSV risk, while COVID-19 booster doses are recommended for priority groups every six to twelve months. PAHO also stressed the importance of simple preventive measures, including handwashing, respiratory etiquette, and staying home when symptomatic, to limit virus transmission.
