Recombinant receptor binding domain (aa 319-591) of SARS-CoV2 Omicron variant BA.1 (Mutations: G339D, S371L, S373P, S375F, K417N, N440K, G446S, S477N, T478K, E484A, Q493K, G496S, Q498R, N501Y, Y505H, T547K), expressed in Expi293 cells and Streptactin-purified. The protein is equipped with a SpyTag (AHIVMVDAYKPTK) at the C-terminus.