A DNA sequence encoding the SARS-CoV-2 (XBB.1.5) Spike S1+S2 trimer (YP_009724390.1, with mutations T19I, del24-26, A27S, V83A, G142D, Y144del, H146Q, Q183E, V213E, G339H, R346T, L368I, S371F, S373P, S375F, T376A, D405N, R408S, K417N, N440K, V445P, G446S, N460K, S477N, T478K, E484A, F486P, F490S, Q498R, N501Y, Y505H, D614G, H655Y, N679K, P681H, R682G, R683S, R685S, N764K, D796Y, F817P, A892P, A899P, A942P, Q954H, K986P, V987P, N969K and furin cleavage site mutants) was expressed with bacteriophage T4 fibritin and a C-terminal polyhistidine tag followed by an AVI tag. The mutations were identified in the SARS-CoV-2 variant (known as variant XBB.1.5).The expressed protein was biotinylated in vivo by the Biotin-Protein ligase (BirA enzyme) which is co-expressed.