Feasibility study to evaluate the correlation between results of a candidate in vitro assay and established in vivo assays for potency determination of Newcastle disease vaccines.

A Newcastle disease virus antigen quantification assay has been developed at CIDC-Lelystad as a candidate in vitro potency test for inactivated Newcastle disease vaccines. In studies performed at CIDC-Lelystad, a high correlation was demonstrated between the results of this candidate in vitro potency assay and the results of the serological potency assay (European Pharmacopoeia monograph 0870; test A). Furthermore, a high correlation between the serological data (Haemagglutination Inhibition-antibody titres) and clinical protection after challenge was demonstrated. The aim of the feasibility study was to confirm the correlation between the results obtained using the candidate in vitro potency assay and the results from both the in vivo potency assays currently prescribed in Ph Eur monograph 0870, in different laboratories and to determine whether a large-scale validation study of the in vitro method should ensue. In the feasibility study three Official Medicines Control Laboratories tested the potency of 5 different inactivated Newcastle disease vaccines and one experimental vaccine, using both of the in vivo methods described in the European Pharmacopoeia and the candidate in vitro method. The 6 vaccine batches represented a quantitative range of Newcastle disease virus antigen content and were produced by different manufacturers. Statistical evaluation of all results indicated that a satisfactory correlation was found in all laboratories between the two types of in vivo tests currently in place, and the candidate in vitro test. An excellent reproducibility of the proposed in vitro method was observed with respect to the ranking of the vaccines included in this study. It is concluded that the results of this feasibility study indicate that a large-scale collaborative study can be organised to validate the in vitro method and the suitability of the reference preparation.