Polypeptides of the p-ORF2 protein of the hepatitis E virus, including at least the amino acid sequence 394-660, numbered in relation to a p-ORF2 protein of 660 amino acids, in which the three cysteines at positions 627, 630 and 638 have been mutated or, for a p-ORF2 protein of different length, at least the amino acid sequence corresponding to amino acids 394-660 of the p-ORF2 protein of 660 amino acids, in which the three cysteines located at the three positions corresponding to positions 627, 630 and 638 of the p-ORF2 protein of 660 amino acids have been mutated. Also, methods for determining the presence of the humoral response or the titer of antibodies directed against the p-ORF2 protein using these polypeptides, and also the use thereof in the context of infection with the hepatitis E virus.