Protective efficacy in chickens against NDV and H5N1 AIV challenges.The protective efficacy of the recombinant viruses against NDVs and AIVs were examined, and the potential of these recombinant viruses to serve as bivalent vaccines was investigated. To determine the protective efficacy of the recombinant virus against highly pathogenic NDV, we challenged chickens with 103 CLD50 of highly pathogenic F48E9 NDV 3 weeks postvaccination (p.v.). As shown in Table 3, chickens immunized with rLa and the recombinant viruses were completely protected from NDV challenge, showing no signs of disease or deaths for two weeks. In contrast, all of the chickens in the control groups died within 3 days.