Since its initial isolation from a turkey flock in Wisconsin, USA, in 1966, the H9N2 subtype of avian influenza virus (AIV) has emerged as a significant threat to the global poultry industry and human health. Over the past two decades, the H9N2 subtype of AIV (abbreviated as H9N2 virus) has spread rapidly worldwide, establishing endemic circulation in numerous countries and regions across Asia, the Middle East, Africa, and Europe. As a primary endemic region for the H9N2 virus, China has experienced widespread transmission and the establishment of local endemicity throughout most of its territory since the virus was first detected in Guangdong Province in 1994. According to data compiled by the World Health Organization (WHO)´s Global Influenza Surveillance and Response System (GISRS), China accounts for over 70?% of the globally reported H9N2 virus isolates, thereby establishing it as the genetic and geographic epicenter of this virus. Since 2016, the H9N2 virus has progressively become the dominant AIV subtype in live poultry markets. The H9N2 virus infects not only birds but also mammals, including humans. Since the first human case of H9N2 virus infection was identified in China in 1998, human infections have gradually increased in recent years.