Epidemiologic Overview and Viral Characteristics of Influenza A(H3N2) Subclade K during the 2025–26 Influenza Season

Po-Han Huang^*, Yung-Ching Lin

2026 Vol.42 No.4

Correspondence Author： Po-Han Huang^*

Abstract：

        This review evaluates the emergence and clinical implications of the influenza A(H3N2) variant subclade K (formerly designated J.2.4.1) during the 2025–26 season. Driven by multiple genetic mutations resulting in significant antigenic drift, subclade K had rapidly spread worldwide. Its emergence as the globally dominant strain was associated with an earlier-than-usual onset of seasonal influenza activity in several countries. In Taiwan, surveillance data indicated that A(H3N2) subclade K had emerged as the dominant strain by September 2025, with the influenza season beginning earlier than in previous years.
        Although antigenic characterization and serological assays suggested a suboptimal immune response to subclade K elicited by the 2025–26 Northern Hemisphere influenza vaccine, raising concerns over a potential vaccine mismatch, preliminary real-world evidence from Europe and the United Kingdom indicated that the current vaccine maintained robust effectiveness against influenza requiring medical attention at the primary care level, and influenza-related emergency department visits and hospitalizations in both pediatric and adult populations. Furthermore, available data suggested that subclade K did not correlate with increased disease severity or resistance to standard antiviral therapeutics. In light of the influenza subclade K outbreak in Taiwan, we recommend maintaining multifaceted epidemiologic and laboratory surveillance and reiterate the critical importance of optimizing vaccination coverage.

Keywords：influenza, H3N2, subclade K, antigenic drift, vaccine mismatch
 

Prevention and Control of Brucellosis following Detection in Goats at a Southern Taiwan Livestock Farm, 2023

Li-Chuan Wu^*, Min-Nan Hung, Ching-Li Lin, Hui-Chen Lin, Min-Cheng Lin

2026 Vol.42 No.4

Correspondence Author： Li-Chuan Wu^*

Abstract：

        In December 2023, routine surveillance by the Ministry of Agriculture detected Brucella infection in three goats at a southern Taiwan livestock farm, marking the first animal brucellosis cases in over 30 years. Local authorities undertook comprehensive investigations of the farm, assessed and monitored all human contacts, implemented animal disease control measures, and conducted environmental disinfection. Human contacts were subjected to health monitoring over a two-month period, while the remaining goats on the farm underwent serological testing every six weeks for a total of three rounds. At the conclusion of the surveillance period, none of the human contacts developed symptoms or signs related to Brucella infection, and no more positive goats were detected on the farm. Brucellosis is a zoonotic disease primarily transmitted through food contaminated with Brucella or the consumption of unpasteurized milk. Laboratory workers, slaughterhouse personnel, and meatpacking plant workers are also at risk of infection through direct contact with or inhalation of the pathogen. While human-to-human transmission is rare, the disease can be effectively contained by implementing appropriate preventive measures, conducting symptomatic surveillance, and ensuring early identification and diagnosis.

Keywords：Brucellosis, zoonotic disease, livestock, undulant fever