Submitted to: Avian Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/2008
Publication Date: 6/18/2008
Citation: Liljebjelke, K.A., King, D.J., Kapczynski, D.R. 2008. Determination of minimum hemagglutinin units in an inactivated Newcastle disease virus vaccine for clinical protection of chickens from exotic Newcastle disease virus challenge. Avian Diseases. 52:260-268. Interpretive Summary: Newcastle disease (ND) is one of the most important viral diseases of poultry worldwide. Vaccination against ND virus is widely practiced in the U.S., with the majority of commercial birds receiving multiple vaccinations during their lifetime. The current U.S. standard potency test for inactivated Newcastle disease vaccines requires a virulent virus challenge. Virulent NDV strains are classified as Select Agents and their use requires specialized facilities and additional personnel suitability requirements not required for other aspects of biological production. The objectives of the present study were to extend the knowledge of vaccine induced protection by inactivated NDV vaccines and utilize that information to develop correlates with vaccinates challenged with exotic Newcastle disease virus thereby eliminating the requirement for a virulent challenge. A correlation of protection was determined based on antigen concentration and antibody levels induced by inactivated ND vaccines prepared with different antigenic content. The results indicate that those parameters can provide the basis of standard potency of inactivated ND vaccines that correlates with 100 % protective immunity from lethal challenge.
Technical Abstract: The potency of inactivated Newcastle disease (ND) vaccines are currently determined using vaccination and challenge of experimental animals. If the minimum amount of killed viral antigen required for clinical protection can be determined using other methods, vaccines meeting these criteria might be considered of adequate potency. The linearity of correlation between the hemagglutination assay (HA) measurement and the 50% embryo infectious dose titer of ND virus (NDV) B1 virus was determined. Correlation between hemagglutinin units (HAU) per vaccine dose, clinical protection, and antibody response was then determined using a vaccinate-and-challenge model similar to the U.S. 9 CFR approved method for testing vaccine potency currently used in the U.S. The dose of an in-house water-in-oil emulsion vaccine formulated with inactivated NDV B1 providing 50% protection was determined to be 600 HA units. A commercial water-in-oil emulsion killed ND vaccine was used for comparison to the in-house emulsion vaccines of know HAU content. These are the first studies to suggest a minimum HAU content for inactivated ND vaccines establishing a dose necessary to ensure potency.