RECOMBINANT MVA VIRUSES CONTAINING AND CAPABLE OF EXPRESSING FOREIGN GENES WHICH IS INSERTED AT THE SITE OF A NATURALLY OCCURING DELETION WITHIN THE MVA GENOME, AND THE USE OF SUCH RECOMBINANT MVA VIRUSES FOR THE PRODUCTION OF POLYPEPTIDES, E.G. ANTIGENS OR THERAPEUTIC AGENTS, AND FOR THE PRODUCTION OF RECOMBINANT VIRUSES FOR VACCINES OR VIRAL VECTORS FOR GENE THERAPY.