A bold update: influenza A viruses are driving the current global flu season, and the trend is set to continue. The World Health Organization (WHO) reported this pattern in a December update, noting that influenza activity has risen worldwide since October, with influenza A predominating in circulation.
In their latest assessment, titled Seasonal influenza – Global situation, WHO linked the uptick to the start of winter in the Northern Hemisphere and a typical seasonal surge in acute respiratory infections from influenza and other respiratory viruses.
Although overall global influenza levels still fall within expected seasonal ranges, several regions have experienced earlier starts and more intense activity than usual, especially involving influenza A (H3N2). In many Northern Hemisphere countries, rates of acute respiratory infections have climbed due to seasonal epidemics caused by influenza, respiratory syncytial virus (RSV), and other common respiratory pathogens.
Predicting the exact onset timing, duration, magnitude, and severity of each seasonal wave remains difficult. Outcomes depend on the specific circulating viruses, population immunity, and environmental conditions.
Some Northern Hemisphere nations have reported early flu season activity without reaching epidemic thresholds, while parts of the Southern Hemisphere have seen above-average virus activity in recent months.
Across temperate, sub-tropical, and tropical regions, detections of H3N2 viruses have risen, making H3N2 the dominant strain since late September.
The WHO also noted that seasonal influenza viruses continue to evolve. Since August 2025, genetic sequence data show an uptick in H3N2 subclade J.2.4.1 (also referred to as K subclade) viruses detected in several countries. These K-subclade variants carry several genetic changes compared with related H3N2 strains, but current epidemiological data do not indicate a rise in disease severity.
Vaccination remains a key protective measure. WHO emphasizes that vaccines are essential, especially for people at high risk of influenza complications and their caregivers. Even if circulating strains differ somewhat from those included in vaccines, Seasonal influenza vaccines can still offer meaningful protection.
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