The disclosure relates to a multi-epitope fusion protein as well as to its use as calibrator and/or control in an in vitro diagnostics immunoassay for detecting HCV core antigen. The multi-epitope fusion protein has two to six different non-overlapping linear peptides present in the amino acid sequence of hepatitis C virus (HCV) core protein, wherein each of the peptides is separated from the other peptides by a spacer consisting of a non-HCV amino acid sequence and having a chaperone amino acid sequence. No further HCV specific amino acid sequences are present in the polypeptide. A further aspect relates to a reagent kit for detecting HCV core antigen containing said multi-epitope fusion protein as calibrator or control or both.