The protective dose of a live recombinant LaSota Newcastle disease virus (NDV)–avian influenza H5 vaccine (rNDV-LS/AI-H5) was determined in broiler chickens with high levels of maternal antibodies against NDV and avian influenza virus (AIV). At hatch the geometric mean titers (GMT) of the chickens' maternal antibodies were 25.1 and 210.3 for NDV and AIV, respectively. At the time of vaccination the GMT was 23.1 for NDV and 27.9 for AIV. The chickens were vaccinated with one drop (0.03 ml) in the eye at 10 days of age as is typical under field conditions. The test chickens received 104.8, 105.8, 106.8, or 107.8 mean chicken embryo infective doses (CEID50) of the rNDV-LS/AI-H5 vaccine. Control chickens were either nonvaccinated, or vaccinated with 105.8 or 106.8 CEID50 of a commercial live LaSota NDV vaccine. Birds were challenged with either the Mexican highly pathogenic avian influenza virus (HPAIV) strain A/Chicken/Queretaro/14588-19/95 (H5N2) or a Mexican velogenic viscerotropic (VV) NDV strain. One hundred percent of the chickens vaccinated with the rNDV-LS/AI-H5 vaccine were protected against HPAIV and VVNDV when a challenge dose of 106.8 EID50 or higher was administered by eye drop. Birds vaccinated with the LaSota NDV vaccine were protected against VVNDV, but not against HPAIV.
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Vol. 54 • No. s1