The H3 set had the most glycosites (16, as shown in File S6) among all HA subtypes, which were mainly contributed by H3N2 and H3N8 virus. The earliest H3 record had only one moderate conservative glycosite (79NCT, e.g. A/equine/Miami/1/1963 (H3N8)) except for six highly conserved glycosites, which is also conserved in most seasonal human H3N2 virus and mammalian H3N8 virus (e.g. A/Denmark/22/2011 (H3N2) or A/equine/ Yokohama/aq79/2011 (H3N8)), but not in subsequent avian H3N1, H3N9 virus (e.g. A/duck/Zhejiang/5/2011 (H3N3) or A/duck/Saitama/2/2009 (H3N8). File S5). Over the last four decades, seasonal human H3N2 viruses have gradually acquired additional glycosites within the globular HA1 [37, 40] . The occurrence of 294NSS has increased the glycosite numbers to 13 in parts of current HA of H3N2 virus from 2010 (A/Singapore/ GP5/2011(H3N2). File S6).