The influenza virus belongs to the Orthomyxoviridae family and is a single-stranded negative-sense RNA virus, categorized into types A, B, C, and D. Its structural features include an outer lipid envelope with two glycoprotein spikes: hemagglutinin (HA) and neuraminidase (NA). The influenza virus primarily replicates within host upper and lower respiratory tract cells, utilizing the viral RNA polymerase to replicate its RNA genome. Viral infection triggers the host's immune response, including antiviral interferon responses. The HA and NA genes of the influenza virus undergo high levels of variation, leading to frequent antigenic variation, which is the main reason for updating influenza vaccines, while also influencing the virus's pathogenicity and epidemic potential.