全球呼吸道病毒活动：每周更新第563号

GLOBAL INFLUENZA SURVEILLANCE AND RESPONSE SYSTEM (GISRS) Co-circulationInfluenza SUMMARY Globally, influenza activity continued to decrease over the past three weeks but positivity remained elevated around 15% in week 4 2026. SARS-CoV-2activity remained low overall. Influenza predominated and positivity was around 15% in the northern hemisphere temperate and subtropical areas and inthe tropical areas. In the southern hemisphere temperate and subtropical areas, influenza and SARS-CoV-2 positivity were both low. [Figures 1a, 1b, 1c qInfluenza Globally, influenza detections continued to decline and influenza A viruses were predominant among influenza detections in week 4. [Figure 2] In the northern hemisphere, influenza percent positivity was elevated (>10%) in countries in North America and Western Africa. Percent positivitywas over 30% in countries in Central America and the Caribbean, Tropical South America, Northern Africa, Europe, and Asia (except Central Asia). In the southern hemisphere, influenza activity remained low overall although elevated positivity (>10%) was reported in single countries in TropicalSouth America, Eastern Africa and South-East Asia; percent positivity was over 30% in single countries in Temperate South America and Oceania. A In the zones with elevated positivity, influenza A(H3N2) was predominant in most of the zones except Central America and the Caribbean, TropicalSouth America and Eastern Africa where there was codominance of influenza A(H1N1)pdm09 and A(H3N2) and B viruses. [Figures 5 and 6] qSARS-CoV-2 Globally, SARS-CoV-2 positivity remained stable and low, with single countries reporting elevated positivity (>10%) in Temperate South Americaand South West Europe. [Figures 7 and 8] qRespiratory Syncytial Virus (RSV) Globally, RSV positivity remained stable and low, with single countries reporting elevated positivity (>10%) in Central America and the Caribbean,Western Africa, Northern and South West Europe and Western Asia. Small increases in activity were reported in single countries in Central Americaand the Caribbean and South West Europe. [Figures 9 and 10] RSV and influenza activity were both elevated in single countries in Central America 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 moderate (2); transmissibility using syndromic data was reported as below seasonal threshold (9), low (15), moderate (8) and high (3). Co-circulation of influenza and SARS-CoV-2 1b) Weekly numbers of influenza andSARS-CoV-2 virus specimens tested and 1d) Weekly numbers of influenza andSARS-CoV-2 virus specimens tested and Influenza SARS-CoV-2 8) Change in proportions of specimens that testedpositive for SARS-CoV-2 (year-week:2026-04) Respiratory syncytial virus 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 is reached 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. Activity summaries are organized by geographical groupings of CATs. These groupings are intended solely for geographic reference and do not imply uniformity in respiratory virustransmission patterns within each group. It is important to note that specimens tested for influenza, SARS-CoV-2, and RSV may not originate from the same sample sources within 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 de