Prevalence and Transmission of Influenza A (H6) Viruses Pose a Potential Threat to Public Health

On March 25, 2024, the clade 2.3.4.4b highly pathogenic influenza H5N1 virus infection was reported in dairy cattle in Texas, USA. As of June 7, 2025, outbreaks of H5N1 virus occurred in more than 1000 dairy farms across 17 states, with a mortality rate of up to 10% in infected cattle. Additionally, the H5N1 virus caused 41 confirmed human infections among dairy workers in 2024. Highly pathogenic influenza viruses pose a persistent threat to global public health, while the potential risks of low pathogenic influenza viruses should not be ignored. Recently, we read with interest the articles published in the Journal of Infection regarding human infections with low pathogenic H3N8, H7N4, H9N2, H10N3, H10N5 and H10N8 subtype influenza viruses. In addition to the aforementioned subtypes, the H6 subtype influenza virus has also garnered significant attention from the scientific community. It is reported that H6 subtype viruses were widely circulating in various avian hosts, including wild, domestic aquatic and terrestrial bird species. Notably, some H6 viruses could cross species barrier to infect mice and ferrets without prior adaptation, and even acquired the ability to bind to human-type receptors. Furthermore, a serological analysis targeting individuals with occupational exposure to poultry in China demonstrated that among 15689 serum samples collected from 22 provinces across mainland China, 63 tested positive for H6 avian influenza virus (AIV). Strikingly, the first human case with H6N1 subtype AIV infection was reported in Taiwan region, China in 2013. These data indicate the extensive host range that the H6 virus can infect, and the virus has resulted in spillover events, posing a potential threat to public health security.