The glycosites of NA can be divided into two types according to the distributed region: two to four highly conserved glycosites are located in the stalk domain in each subtype; two conserved glycosites and most middle-low conserved glycosites are mainly located in the global domain, which are near the tip of NA, the connection of the global and stalk domains, or the antigenic sites. The glycosite of 146N is conservative in all NA subtypes (e.g., 146NDT in A/Boston/20/2008(H3N2), 144NGT in A/duck/ Taiwan/4201/99(H7N7) or 146NGT in /Viet Nam/1203/ 2004(H5N1)). It has been shown that the N-glycan at this glycosite affects NA enzymatic activity, causing a 20-fold decrease in activity [58] . Similar to the description of HAs, a large number of H1N1, H3N2, H5N1, H7N2 and H9N2 viruses have accumulated numerous glycosites in N1 and N2, especially in the global domain, mainly participating in immune evasion. Moreover, one conserved glycosite, 12NTT (Conservative rate: 93%, e.g., A/ turkey/Italy/3807/2004 (H7N3)), located in the transmembrane domain in N3 and N10, requires further investigation [59] .