Collaborative study for the establishment of tetanus vaccine (adsorbed) Third International Standard and European Pharmacopoeia Biological Reference Preparation batch no. 2.

The aim of the present collaborative study was to calibrate two candidate replacement standards for tetanus vaccine for human use in the terms of the Second International Standard (IS) for Tetanus Toxoid, Adsorbed (TEXA-2) using challenge potency assays in guinea pigs and mice and to establish the 3rd IS and the Ph. Eur. BRP batch 2. Two test preparations (coded B and C) were included as candidate replacement for TEXA-2 and Ph. Eur. BRP batch 1 (EBRP-1). This project was run as a joint WHO/Ph. Eur. study. Twenty-seven laboratories representing nineteen countries participated in the study. Twenty-three laboratories performed assays in mice (11 laboratories performed lethal, 11 paralysis, and one serology assays) and fourteen laboratories performed assays in guinea pigs (10 laboratories performed lethal and 4 paralysis assays). Estimates of potency, expressed in ampoule of TEXA-2 per ampoule of candidate replacement standards were two-fold higher in mice than in guinea pigs. However, using the assumed relationship between TEXA-1 and TEXA-2 in mice and guinea pigs (Lyng and Nyerges, 1984), potency estimates for candidate replacement standards (sample coded B and C), in terms of TEXA-1, gives estimates which are similar in both animal models. Stability was assessed within the collaborative study for candidate standard B. On the basis of this collaborative study, the ECBS of WHO has established the candidate material coded B as the Third IS for Tetanus Toxoid, Adsorbed, with an assigned unitage of 469 IU/ampoule, based on its calibration by guinea pig challenge assays (WHO report BS/00.1932). Further studies were organised to assess which of the two candidate standards is most suitable as replacement for EBRP-1. Manufacturers were asked to include candidate B and candidate C in their routine quality control potency assays of tetanus vaccines in order to assess the impact of the use of either preparation on their calibration results. The features and results of this additional phase are described at the end of this report in a separate section entitled "Choice of replacement batch for EBRP-1". Based on these results, at the session in March 2001, the Ph. Eur. Commission adopted candidate B as the Tetanus vaccine (adsorbed) Ph. Eur. BRP Batch 2 with assigned potencies of 469 IU/ampoule for the guinea pig assays and 496 IU/ampoule for the mouse assays.