New Newcastle disease viruses (NDVs) have been circulating among poultry flocks in several Southeast (SE) Asian countries since the mid-2000s. This study analyzes whether the NDV vaccine strain, NDRL0901, protects against genotype VIIh of NDV. The efficacy of the NDRL0901 vaccine was tested in week-old and three-week-old specific pathogen free (SPF) chickens. Week-old chickens that had been vaccinated had geometric mean hemagglutination inhibition (HI) titers of 2^4.1 to 2^4.7 two weeks after vaccination. The vaccinated birds were completely protected against potentially fatal clinical disease from both the MY3519/2010 and VN5/2007 NDV strains, which were administered via eye drops. No virus was detected in the vaccinated birds, regardless of the challenge virus. When three-week-old SPF chickens were vaccinated, the birds had geometric mean HI titers of 2^6.3 two weeks after vaccination. The NDRL0901 vaccine provided complete clinical protection against fatal challenges from the NDV isolate, KN5/2011, which was administered via the intramuscular route. No virus shedding was detected in the vaccinated birds after administration of the challenge virus. Our results indicate that locally developed NDV vaccines using NDRL0901 vaccine strain could provide complete protection against the emergent NDV genotype VII in SE Asia.

Key words: Newcastle disease vaccine, Newcastle disease virus, Protection, Southeast (SE) Asia