Abstract
The Central Veterinary Laboratory, Weybridge, England, was requested by the WHO Expert Committee on Biological Standardization to arrange a collaborative assay to test a freeze-dried preparation of live Newcastle disease vaccine (Hitchner B1 strain) for its suitability to serve as an international reference preparation. Nine laboratories in 8 countries assayed the vaccine against a number of test preparations of different vaccine strains. On the basis of the results obtained, the material has been established as the International Reference Preparation of Newcastle Disease Vaccine (Live) and is considered suitable for standardizing the titration of the Hitchner B1 strain and related strains of virus.
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