Global Respiratory Virus Activity: Weekly Update N° 577

Overview

In week 18 2026, influenza positivity remained below 10% and SARS-CoV-2 activity remained low globally and in the northern hemisphere temperate and subtropical areas, tropical areas and the southern hemisphere temperate and subtropical areas. RSV positivity also remained stable and low globally.

Influenza

Globally, influenza detections remained low in week 18 and influenza B viruses were predominant among influenza detections.

In the northern hemisphere, influenza percent positivity was elevated (>10%) in some countries in Central America and the Caribbean, Western and Eastern Africa and Southern Asia and in a single country in Eastern Asia. Percent positivity was over 30% in a single country in Western Africa. Small increases in activity were observed in single countries in Central America and the Caribbean, Eastern Africa and Southern Asia and in two countries in Western Africa.

In the southern hemisphere, influenza activity remained low overall although elevated positivity (>10%) was reported in some countries in Temperate South America and Eastern Africa and in single countries in Southern Africa and South-East Asia. Percent positivity was over 30% in a single country in Tropical South America. Small increases in activity were observed in single countries in Tropical and Temperate South America, Southern Africa and Oceania.

In the zones with elevated positivity, influenza A(H3N2) was predominant in Central America and the Caribbean, Eastern Africa, Tropical and Temperate South America, and Southern Africa. Influenza B was predominant in Western Africa and Eastern Asia. Influenza A(H1N1)pdm09 and A(H3N2) were codominant in Southern Asia and influenza A(H3N2) and B were codominant in South-East Asia.

SARS-CoV-2

Globally, SARS-CoV-2 positivity remained stable and low across reporting countries, with no countries reporting elevated activity (>10%). Small increases in activity were observed in single countries in Central America and the Caribbean and Southern Asia.

Respiratory Syncytial Virus (RSV)

Globally, RSV positivity remained stable and low, with elevated positivity (>10%) reported in a few countries in Eastern Europe and Eastern Africa and in single countries in Central America and the Caribbean, Tropical South America, Northern Europe and Southern Asia. Percent positivity was over 30% in a single country in Eastern Africa. Small increases in activity were observed in single countries in Tropical South America and Southern Asia. RSV and influenza activity were both elevated in countries in Eastern Africa and Southern Asia.

Severity assessment

The severity assessments here are reported from countries, areas and territories. Assessments for transmissibility can be reported based on syndromic parameters and/or influenza-specific parameters. In the northern hemisphere temperate and subtropical areas, influenza-specific transmissibility was reported as below seasonal threshold (23); low (8) and moderate (1); transmissibility using syndromic data was reported as below seasonal threshold (24) and moderate (1). Influenza-specific transmissibility was reported as low in a single country in the southern hemisphere temperate and subtropical areas.  

WHO encourages countries, especially those that have received the multiplex influenza and SARS-CoV-2 reagent kits from GISRS, to conduct integrated surveillance of influenza and SARS-CoV-2 and report epidemiological and laboratory information in a timely manner to established regional and global platforms. The guidance can be found here.

Starting with report #501, the Global Respiratory Virus Activity Weekly Update included data from sentinel surveillance and other types of systematically conducted virologic surveillance. Countries, areas, and territories use a variety of approaches to monitor respiratory virus activity and data in this report may vary from surveillance reports posted elsewhere. Analyses stratified by source of surveillance is available through Respimart.