The invention relates to isolated recombinant analogues of flavivirus E-proteins comprising an analogue of a flavivirus E-protein fusion loop, wherein the analogue of the flavivirus E-protein fusion loop comprises at least one glycosylation site for an N-linked glycan that is not present in a natural flavivirus E-protein fusion loop sequence, wherein the at least one glycosylation site is an N-linked glycosylation sequon (Asn-X-Ser/Thr) and the Asn (N) residue of the sequon occupies any of positions 98-110 (DRGWGNGCGLFGK) of the natural flavivirus E-protein fusion loop amino acid sequence, wherein X is any amino acid residue except proline and Ser/Thr denotes a serine or threonine residue for use in an in vitro method for specific detection of anti-flavivirus antibody, diagnosis of flavivirus infection and/or to investigate exposure to flavivirus.
