While there is typically 100% survivability in birds challenged with vNDV under experimental conditions, either with
vaccines formulated with a strain homologous or heterologous (different genotype) to the challenge virus,
vaccine deficiencies are often noted in the field. We have developed an improved and more stringent protocol to experimentally evaluate live NDV
vaccines, and showed for the first time under experimental conditions that a statistically significant reduction in mortality can be detected with genotype matched
vaccines. Using both
vaccine evaluation protocols (traditional and improved), birds were challenged with a vNDV of genotype XIII and the efficacy of live heterologous (genotype II) and homologous (genotype XIII) NDV
vaccines was compared. Under traditional vaccination conditions there were no differences in survival upon challenge, but the homologous
vaccine induced significantly higher levels of
antibodies specific to the challenge virus. With the more stringent challenge system (multiple
vaccine doses and early challenge with high titers of vNDV), the birds administered the homologous
vaccine had superior humoral responses, reduced clinical signs, and reduced mortality levels than those vaccinated with the heterologous
vaccine. These results provide basis for the implementation of more sensitive methods to evaluate
vaccine efficacy.