Structurally, the capsid monomer is divided into three domains. The shell domain (S) forms the core of the particle and the protruding domain (P) extends away from the core. The P domain is further subdivided into the P1 subdomain (residues 226-278 and 406-520) and the P2 subdomain (residues 279-405) [11] . The P2 subdomain is the most exposed region of the viral particle and is well positioned to interact with potential neutralizing antibodies and histoblood group antigen (HBGA) ligands [13] [14] [15] [16] [17] . Previous studies have shown that the P2 subdomain of the major capsid protein of GII.4 strains is evolving rapidly, resulting in new epidemic strains with altered carbohydrate ligand binding properties and antigenicity [13, [18] [19] [20] [21] [22] [23] .