Report of a collaborative study to assess the suitability of a replacement International Standard for Oral Polio Vaccine

Overview

The potency of a trivalent oral poliovaccine (OPV) preparation was assessed by collaborative study as a candidate replacement for the current International Standard (NIBSC reference 85/659). Thirteen laboratories participated in the study and were drawn from five OPV manufacturers and eight National Control Authorities. Five samples were assessed in the study; the current IS, the candidate replacement (NIBSC reference 02/306), the European Pharmacopoeia Biological Reference Preparation, a commercial vaccine and the same vaccine that had been heat stressed. The candidate preparation was tested as a coded duplicate sample in the study. Laboratories were allowed to use their own anti-sera for neutralization in the test (for which nine elected to do so) but were also asked to include the current NIBSC monoclonals which were freeze dried preparations. The overall levels of within assay variability were 0.18 log10 TCID50 (average root mean square difference in log10 titres between duplicate samples C and D). The within laboratory variation gave an average coefficient of variation of 2.50% (between log10 estimates of the same sample across assays). These figures correspond with previous studies and indicate a high level of consistency within laboratories. For all poliovirus types in all study samples the range of values obtained between laboratories were all within 0.5 log10 TCID50 of the mean – indicating good consistency between laboratories. An overall potency obtained for the candidate 2nd IS was 7.51, 6.51, 6.87 and 7.66 log10 TCID50/ml for type 1, 2, 3 and total virus content respectively. There were no problems encountered in the use of the candidate 2nd IS and all other samples behaved as predicted. No substantial differences were obtained with the NIBSC monoclonal antibodies or the in-house antisera.