The invention provides peptide epitopes for use in the prevention and/or treatment of influenza or for the development of such treatment or vaccine against influenza. The invention also relates to a method for evaluating the potential of a chemical entity, such as an antibody, to bind to a peptide epitope derived from the divalent sialoside binding site of hemagglutinin protein of influenza virus, and to conjugates containing one or more such peptide epitopes. The peptide epitopes of the invention are cyclic peptides comprising a 7-mer peptide derived from H1, H3 or H5 hemagglutinin of influenza virus. The 7-mer peptide has a sequence corresponding to the loop sequence at positions 220- 226 of X31-hemagglutinin.