Influenza activity has been increasing globally since October 2025, with several countries reporting an early start to the flu season. Health surveillance data shows that influenza A(H3N2) viruses have emerged as the dominant strain in circulation across multiple regions.
In many countries of the northern hemisphere, levels of acute respiratory infections typically rise during this time of year.
These seasonal increases are usually driven by respiratory pathogens such as influenza viruses, respiratory syncytial virus (RSV) and other common respiratory
infections.
Recent months, however, have seen a sharper rise in seasonal influenza activity worldwide, with a growing proportion of A(H3N2) viruses being detected.
Seasonal influenza, commonly known as the flu, is an acute respiratory illness caused by influenza viruses that circulate globally throughout the year. The illness can range from mild to severe and, in some cases, lead to hospitalization or death. There are four types of influenza viruses—A,B, C and D—of which influenza A and B are responsible for seasonal epidemics.
The A(H3N2) strain, described as more aggressive, has been linked to widespread outbreaks and has sickened millions globally. Common symptoms include high fever, persistent cough, body aches, and in some cases breathlessness or chest pain, with fever lasting more than three days.
Last month, the Pan American Health Organization and the World Health Organization (PAHO/WHO) issued an alert warning of a possible early or more intense circulation of respiratory viruses during the 2025–26 season compared to previous years.
South Asia
According to the alert, influenza detections in the WHO South-East Asia Region began increasing from June 2025, peaked in August, and have generally remained low since, with some exceptions. In Thailand,influenza activity—predominantly A(H3N2)—rose in October and November. Similar increases were recorded in Bangladesh from July and in Sri Lanka from October.While A(H3N2) activity has increased across the region, 22 sequences of subclade K have been reported to the global influenza database GISAID from Nepal (1), India (4), and Thailand (17).In India, recent media reports indicate a noticeable rise in flu-like illnesses and respiratory infections, particularly in Delhi, where A(H3N2) has been detected in some cases. Bengaluru has also reported a steady increase in seasonal influenza and other respiratory infections, with H3N2 emerging as the dominant strain.In China, the National Health Commission reported that influenza activity has declined for four consecutive weeks, with recent testing showing common respiratory pathogens and no evidence of any new infectious disease. Meanwhile, the National Public Health Laboratory, Nepal stated that influenza cases began rising from September 2025, with the virus positivity rate recorded at around 16 percent.
Sharp Increases in West
In the United States by end of December 2025, at least 7.5 million people had been infected with influenza, with over 3,100 deaths, largely attributed to influenza A(H3N2).Canada has also reported intense influenza transmission during the 2025–26 season. By the end of 2025, the national influenza positivity rate reached 32.4 percent, raising concerns over the early start of the season. Authorities noted rapid increases in cases and a high number of outpatient visits, particularly among children.
Southern Hemisphere and Europe
The PAHO/WHO alert also mentioned that in temperate and sub-tropical regions of the southern hemisphere, influenza activity generally declined from June 2025 and remained low through August. A slight increase has been observed since September. The influenza season in these regions has been prolonged, mainly due to continued circulation of A(H3N2).In Chile, the 2025 influenza season followed a bimodal pattern, with influenza A circulating throughout the year. Activity began earlier than in previous seasons, with an initial peak around week 18, when
A(H1N1)pdm09 was the predominant strain.During the final weeks of 2025, a high number of patients seeking primary care for respiratory symptoms was reported across 21 European Union countries. In England, influenza circulation and hospitalisations increased early and rapidly during the 2025–26 season.
Preparedness and Vaccination
In light of these trends, PAHO/WHO has urged countries to strengthen health system preparedness and adjust service plans in anticipation of seasonal influenza and RSV. National health authorities and WHO have also emphasised that vaccination remains one of the most effective public health measures to prevent severe illness, particularly among high-risk groups and caregivers. Early estimates suggest that even where genetic differences
exist between circulating viruses and vaccine strains, seasonal influenza vaccines can still provide protection against severe disease and other circulating strains.
Leave a Reply