The present invention relates to a conjugate comprising an oligo- or polysaccharide selected from the group consisting of: (X)x-{BCDA}n-(Y)y (X)x-{CDAB}n-(Y)y (X)x-{DABC}n-(Y)y (X)x-{ABCD}n-(Y)yWherein A, B, C, D, X and Y, x, y and n are as defined in claim 1,said oligo- or polysaccharide being covalently bound to a carrier.