Provided is a polypeptide having no more than 100 amino acids, which polypeptide comprises one or more sequences having at least 60% homology with any of SEQ ID 1-6, or comprises two or more epitopes having 7 amino acids or more, each epitope having at least 60% homology with a sub-sequence of any of SEQ ID 1-6 that has the same length as the epitope: SEQ ID 1DLEALMEWLKTRPILSPLTKGILGFVFTLTVP SEQ ID 2LLYCLMVMYLNPGNYSMQVKLGTLCALCEKQASHS SEQ ID 3DLIFLARSALILRGSVAHKSC SEQ ID 4PGIADIEDLTLLARSMVVVRP SEQ ID 5LLIDGTASLSPGMMMGMFNMLSTVLGVSILNLGQ SEQ ID 6IIGILHLILWILDRLFFKCIYRLF wherein, the polypeptide is immunogenic in a vertebrate expressing a major histocompatibility complex (MHC) allele, and wherein the polypeptide is not a complete influenza virus protein.