Validation of a candidate in vitro potency assay for inactivated Newcastle disease vaccines

An NDV-HN antigen quantification assay has been developed as a candidate in vitro batch potency assay for inactivated vaccines. The assay consists of extraction of the viral antigens from the oil emulsion vaccines and quantification of the NDV-HN in a DAS-EUSA. After optimisation and preliminary validation, large stocks of lyophilised test reagents were prepared. Stability studies showed that there was no decrease in reactivity of the reagents in one year at -20 degrees after lyophilisation. Also in accelerated stability studies no decrease in reactivity was found after storage at higher temperatures. Antigen recovery, accuracy of the assay and specificity of the assay were found to be satisfactory in an in-house validation study. The intermediate precision was good to very good with coefficient of variation (CV) values that were always below 15%. The transferability of the test protocols has been studied in a pre-validation study in which three laboratories from two different countries participated. The protocols and the assay could be transferred to other laboratories without difficulty. Furthermore, vaccines with low and high potency as well as negative controls were identified by all participants. Finally between-assay as well as between-laboratory variation was satisfactory with CV-values of 0 to 30.