An isolated polypeptide comprising an amino acid sequence corresponding to the amino acid residues forming a full or partial alpha-helical domain, the hinge domain, the beta-triple spiral domain and afull or partial globular head domain of an avian reovirus sigma C protein, and lacking the amino acid sequence that is N-terminal to said alpha-helical domain is provided. Furthermore, a vaccine comprising, or a viral vector expressing, at least one of the isolated polypeptides of the present invention is provided.