Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 51 (26 December 2025)

Regional Situation: Influenza activity in the Americas continues an upward trend, mainly driven by activity in the Northern Hemisphere, with a regional positivity of 16.2%. Influenza A(H3N2) continues to predominate among subtyped samples in all regions, except in the Andean subregion. RSV circulation remains at low levels (<1%), while SARS-CoV-2 positivity continues to decline, reaching 5.4%. In North America, influenza circulation is likely near its peak, with a positivity of 22%. RSV activity remains low, with a slight increase to 2.2%, while SARS-CoV-2 positivity decreased to 5.2%. In the Caribbean, influenza circulation is elevated, with a positivity of 34%. RSV activity continues to decline, reaching 7%, while SARS-CoV-2 remains at low levels (<1%). In Central America, influenza activity remained stable over the past four epidemiological weeks (EWs), with a positivity of approximately 12.2%. SARS-CoV-2 circulation remained low and stable, while RSV activity remained elevated at 10.6%. In the Andean subregion, influenza activity stabilized over the past three EWs at a positivity of 7.2%, while RSV circulation continued to increase, reaching 5.8%. SARS-CoV-2 circulation increased compared with the previous two EWs, reaching a positivity of 5.1%. In Brazil and the Southern Cone, influenza activity decreased compared with the previous EW, with a positivity of 12.6%. RSV circulation remains at interseasonal levels (1.1%), while SARS-CoV-2 activity remained stable, at 8.4%. Circulation of other respiratory viruses (ORVs) has continued to decline since early October, with a regional positivity of 2.7%. Rhinovirus and parainfluenza are the most frequently detected ORVs.