Influenza Update N° 541

Overview

^{Published 28 August 2025 | For reporting Week 33, ending 17 August 2025}

Influenza

• Globally, influenza activity remained low, with influenza A viruses continuing to predominate. Different patterns were observed across hemispheres and transmission zones.
• In the Southern hemisphere, influenza activity remained stable in most reporting countries with an increase in activity observed in a single country in Oceania. Influenza positivity remained elevated (>10%) in South-East Asia and Oceania.
• In the Northern hemisphere, over the past few weeks, influenza activity remained low and stable in most transmission zones. Influenza positivity was elevated in Central America and the Caribbean, Western and Eastern Africa, Southern and South-East Asia and percent positivity was over 30% in some countries. An increase in activity was observed in Tropical South America, Northern Europe and South-East Asia.
• In the transmission zones with elevated positivity, influenza A(H1N1)pdm09 predominated in Central America and the Caribbean, Western Africa and Oceania whilst influenza A(H3N2) was the predominant circulating virus in Southern Asia and South-East Asia. In Eastern Africa, influenza A and B viruses were detected in similar proportion. 

SARS-CoV-2

• Globally, SARS-CoV-2 positivity remained at low levels but increased slightly, with a few countries reporting elevated positivity (>10%) in Central America and the Caribbean, Europe, Western, Southern and Eastern Asia with increases in activity reported in some countries in each of these zones apart from Southern Asia. An increase in activity was also observed in a single country in Tropical South America.
  

Respiratory Syncytial Virus (RSV)

• Positivity remained elevated in some countries in Central America and the Caribbean, Tropical and Temperate South America where positivity rates were over 30% in a few countries. RSV positivity remained stable and low across the majority of reporting countries, with small increases in activity reported only in Central America and the Caribbean.

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 https://www.who.int/publications/i/item/WHO-2019-nCoV-integrated_sentinel_surveillance-2022.1.
 

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.