Chimeric avian paramyxovirus-based vector immunization against highly pathogenic avian influenza followed by conventional Newcastle disease vaccination eliminates lack of protection from virulent ND virus

Recently, we described a chimeric, hemagglutinin of highly pathogenic avian influenza virus (HPAIV) H5 expressing Newcastle disease virus (NDV)-based vector vaccine (chNDVFHNPMV8H5) in which NDV envelope glycoproteins were replaced by those of avian paramyxovirus-8 (APMV-8). This chimeric vaccine induced solid protection against lethal HPAIV H5N1 even in chickens with maternal antibodies against NDV (MDA+). However, due to the absence of the major NDV immunogens it failed to induce protection against Newcastle disease (ND). Here, we report on protection of MDA+ chickens against HPAI H5N1 and ND, by vaccination with chNDVFHNPMV8H5 either on day 1 or day seven after hatch, and subsequent immunization with live attenuated NDV seven days later. Vaccination was well tolerated and three weeks after immunization, challenge infections with highly pathogenic NDV as well as HPAIV H5N1 were carried out. All animals remained healthy without exhibiting any clinical signs, whereas non-vaccinated animals showed morbidity and mortality. Therefore, vaccination with chNDVFHNPMV8H5 can be followed by NDV vaccination to protect chickens from HPAIV as well as NDV, indicating that the antibody response against chNDVFHNPMV8H5 does not interfere with live ND vaccination.