Regional Update, Influenza and Other Respiratory Viruses. Epidemiological Week 49 (12 December 2025)

Regional Situation: Influenza activity in the Americas continues an upward trend, mainly driven by activity in the Northern Hemisphere, with a positivity of 8.8%. Influenza A(H3N2) predominated among subtyped samples in all regions, except in the Andean subregion, where influenza A(H1N1)pdm09 predominated. RSV circulation remains at low levels, with a positivity <1% in the last epidemiological week (EW), while SARS-CoV-2 shows a downward trend with a positivity of 6.4%. In North America, influenza positivity reached 10.6%, showing a sustained steep increase over the past four weeks. RSV activity remains low and relatively stable, with a slight increase, while SARS-CoV-2 positivity remained close to 6%, consistent with the previous EW. In the Caribbean, influenza circulation continued to increase, reaching a positivity of 18.7%. RSV activity remained elevated but showed a downward trend, with a positivity of 15.7%, while SARS-CoV-2 remained at low levels, with a positivity below 1%. In Central America, influenza activity showed a pronounced increase over the past two EW, reaching a positivity of 15.1%. SARS-CoV-2 remained at low and stable levels, while RSV circulation remained elevated at 14.9%. In the Andean subregion, influenza A and RSV activity increased this week to 6.8% and 4.8% positivity, respectively, while remaining relatively stable compared with the previous four weeks. SARS-CoV-2 circulation decreased compared with the previous two EWs, reaching a positivity of 3.9%. In Brazil and the Southern Cone, influenza activity has continued to show an upward trend since early September, reaching a positivity of 13.0%. RSV circulation remains at interseasonal levels, while SARS-CoV-2 activity remained stable, with a positivity of 8.1%. Circulation of other respiratory viruses (ORV) decreased to 3.3% at the regional level, with rhinovirus and parainfluenza being the most frequently detected ORVs.