The present invention relates to recombinant Newcastle disease viruses (NDVrs) with an inserted transcriptional unit which is foreign to its genome and codes for the synthesis of immunomodulating proteins. These systems offer excellent protection results and significantly reduce the excreted viral charge (post-vaccination and post-challenge) in poultry immunised several weeks after being challenged with a velogenic strain of Newcastle virus. In addition these vaccines protect poultry against other pathogenic agents for a long period of time since they induce an increase in the levels of immunomodulating proteins which is reflected in a boost of the immune response of the host and in the promotion of an effective humoral and cellular immune response.
