Immunogenic compositions comprising an immunogenic polypeptide and a pharmaceutically acceptable vehicle are described. The immunogenic polypeptide comprises the amino acid sequence Xaa-Thr-Xaa-Val-Thr-Gly-Gly-Xaa-Ala-Ala-Arg-Thr-Thr-Xaa-Gly-Xaa-Xaa-Ser-L- eu-Phe-Xaa-Xaa-Gly-Xaa-Ser-Gln-Xaa-Ile-Gln-Leu-Ile (SEQ ID NO:8). The immunogenic polypeptide can be coupled to a pharmaceutically acceptable carrier, such as a diphtheria toxoid.