HA and NA have a distribution ratio of 4:1 on the influenza viral envelop and maintain the basic functions of host recognition, infection and viral diffusion [26] . Various studies have reported that some of the factors that influence HA include the number of the basic residues in the HA0 cleavage site, the mutation of key residues in the RBD, the changing of antigenic sites or Nglycosylation sites (glycosites) and the variation of the topology of N-glycan structures [15, 27] . Meanwhile, the factors that influence NA include deletion of the stalk domain, the mutations drugresistance, as well as the changing of antigen sites or glycosites and the variation of the topology of N-glycan structures [28] . As a kind of glycan-binding protein (GBP), HA works with NA, which functions as an exoglycosidase, cooperatively. Only by achieving a dynamic equilibrium between attaching to the host and releasing progeny virions can the IVs gain a long-term mechanism for infection and diffusion.