Collaborative study for the establishment of the Ph. Eur. BRP for oral poliomyelitis vaccine (OPV) Batch 3 for use in the potency assay.

A collaborative study was initiated by the European Directorate for the Quality of Medicines (EDQM) with the goal to calibrate the trivalent candidate European Pharmacopoeia Biological Reference Preparation (BRP) for oral poliomyelitis vaccine (OPV) Batch 3 against the 1st International Standard (IS) for OPV and to establish the material as a working standard. The material is a commercial trivalent stabilised oral poliomyelitis vaccine, consisting of Sabin strains of live attenuated poliovirus types 1, 2 and 3. The new standard is meant to replace the current European Pharmacopoeia BRP for OPV Batch 2, the stocks of which will soon be depleted. Fourteen laboratories participated in the study. Three samples had to be assayed (1st IS, BRP Batch 2, candidate BRP Batch 3). The potency of each virus type in each preparation had to be estimated by using either common monoclonal anti-polio antibody sera and/or the participant's routinely used antisera for neutralizing two of the three virus types present in the trivalent vaccine. In addition the total virus content had to be determined. From the raw data returned, log10 CCID50/ml values were calculated using the probit method (CCID50 is the dose infecting 50% of the cell cultures). The precision (intra-assay variation), repeatability (intralaboratory variation) and reproducibility (inter-laboratory variation) were assessed as absolute titres and as the adjusted titres (potencies of the test samples calculated relative to the 1st IS). An analysis of variance was performed to determine if there were significant differences between assays using mono- or polyclonal antisera. The precision, determined as the width of the uncorrected confidence limits taken across all assays within laboratories, varied on average from +/- 0.13 to +/- 0.34. The repeatability (uncorrected titres) standard deviation varied from 0.08 to 0.27 and was on average 0.174. The repeatability (corrected titres) standard deviation varied from 0.11 to 0.33 and was on average 0.176. In both cases the repeatability standard deviation was very similar when compared between types, between antisera and between samples. None of these differences were statistically significant. The reproducibility (for the corrected titres) was analysed by calculating the standard deviation of the laboratory means which ranged from 0.10 to 0.21 and was on average 0.151. For the corrected titres there is no significant indication that the antiserum type used for neutralisation affects the potency estimate. The study shows that the candidate BRP Batch 3 is suitable as a reference substance and, based on the current results, 6.99, 6.06, 6.83 and 7.20 log10 CCID50/ml are the potencies assigned for Types 1, 2, 3 and total virus content, respectively. Stability data indicate that the candidate material is stable when stored at -20 degrees C. Nonetheless the stability of the new reference preparation will be closely monitored. The candidate material was adopted by the European Pharmacopoeia Commission at its session in March 2002 as European Pharmacopoeia OPV BRP Batch 3.