Global Respiratory Virus Activity: Weekly Update No. 576

GLOBAL INFLUENZA SURVEILLANCE AND RESPONSE SYSTEM (GISRS) Co-circulationInfluenza SUMMARY In week 17 2026, influenza positivity remained below 10% and SARS-CoV-2 activity remained low globally and in the northern hemisphere temperate andsubtropical areas, tropical areas and the southern hemisphere temperate and subtropical areas. [Figures 1a, 1b, 1c and 1d] RSV positivity also remained qInfluenza Globally, influenza detections remained low in week 17 and influenza B viruses were predominant among influenza detections. [Figure 2] In the northern hemisphere, influenza percent positivity was elevated (>10%) in countries in Central America and the Caribbean and Southern Asia,and in single countries in Western and Eastern Africa, and South-East and Eastern Asia. No increases in activity were observed. [Figures 3 and 4] In the southern hemisphere, influenza activity remained low overall although elevated positivity (>10%) was reported in some countries in TemperateSouth America and Eastern Africa and in single countries in Tropical South America, Southern Africa and South-East Asia. Percent positivity was In the zones with elevated positivity, influenza A(H3N2) was predominant in Central America and the Caribbean, Tropical and Temperate South Amer-ica, Eastern and Southern Africa, and Southern Asia. Influenza B was predominant in Western Africa and South-East and Eastern Asia. [Figures 5 and 6] qSARS-CoV-2 Globally, SARS-CoV-2 positivity remained stable and low across reporting countries, with a single country reporting elevated activity (>10%) inWestern Asia. A small increase was observed in a single country in Southern Asia. [Figures 7 and 8] qRespiratory Syncytial Virus (RSV)Globally, RSV positivity remained stable and low, with elevated positivity (>10%) reported in a few countries in Tropical South America, Eastern Europe and Eastern Africa, and in single countries in Central America and the Caribbean, Northern Europe, Northern Africa and Western Asia. qSeverity assessment The severity assessments here are reported from countries, areas and territories. Assessments for transmissibility can be reported based on syndromicparameters and/or influenza-specific parameters. In the northern hemisphere temperate and subtropical areas, influenza-specific transmissibility wasreported as below seasonal threshold (25); low (7) and moderate (2); transmissibility using syndromic data was reported as below seasonal threshold Co-circulation of influenza and SARS-CoV-2 1b) Weekly numbers of influenza andSARS-CoV-2 virus specimens tested and 1c) Weekly numbers of influenza andSARS-CoV-2 virus specimens tested and Influenza SARS-CoV-2 Respiratory syncytial virus 10) Change in proportions of specimens that testedpositive for RSV (year-week:2026-17) Severity assessment Additional information Data and methods The data presented in this report originates from virologic surveillance conducted by countries, areas, and territories (CATs) and submitted to WHO FluNet through participation orcollaboration with the Global Influenza Surveillance and Response System (GISRS). These CATs employ diverse methodologies to monitor respiratory virus activity, which may resultin variations between this report and other surveillance summaries published elsewhere. To assess trends, the proportion of specimens tested positive for influenza or SARS-CoV-2 was smoothed over a 3-weeks period. This analysis includes only countries that tested 10 ormore specimens in at least two of the three weeks. Weekly changes in the smoothed positivity rate for each virus were calculated as absolute differences from the previous week. These The influenza transmission zones map is based on data aggregated over a 3-weeks period, moving backward from the current week until a minimum threshold of 100 tested samples isreached within each influenza transmission zone. Pie charts are displayed on the map only if the total percent positivity in a influenza transmission zones map is 20% or higher. Alltrend analyses are based on ISO 8601 calendar week numbering. Severity assessments: The severity assessments here are reported from countries, areas and territories.WHO’s Pandemic influenza severity assessment (PISA): a WHO guide to assess the severityof influenza in seasonal epidemics and pandemics, 2nd ed outlines the methods for which countries, areas and territories can derive these severity assessments. Assessments fortransmissibility can be reported based on syndromic parameters and/or influenza-specific parameters. Countries, areas and territories may not provide assessments year-round. The assessments may be revised over time if there is retrospective/delayed reporting or updating of previouslyreported data. These assessments are made in the context of historical data from the country making the assessment and thus are not comparable between countries. Assessments may The quality and consistency of influenza surveillance data are influenced by c