Quality control of inactivated erysipelas vaccines: results of an international collaborative study to establish a new regulatory test.

According to the specifications of the European Pharmacopoeia (Ph. Eur.) monograph (Swine Erysipelas Vaccine (Inactivated), Monograph no. 64, European Pharmacopoeia, 3rd edn., 1997) on erysipelas vaccines for veterinary use, batch potency is estimated in a multi-dilution assay after immunisation and infection of mice. Recently, we described a serological assay system (ELISA) which has the potential to replace this challenge-based model (Beckmann R, Cussler K. Wirksamkeitsprüfung von Rotlaufimpfstoffen an der Labormaus. ELISA kontra Infektionsversuch. ALTEX 1994;Suppl. 1:39-45; Rosskopf-Streicher U, Johannes S, Hausleithner D, Gyra H, Cussler K. Suitability of an ELISA for the batch potency test in laboratory mice. Pharmeuropa BIO 1998;1:65-70). The humoral immune response is quantified in pooled sera of ten mice three weeks after immunisation. The results are expressed as relative potency (RP) in comparison to a reference serum. After a pre-validation study had been performed with success (Rosskopf-Streicher U, Johannes S, Wilhelm M, Gyra H, Cussler K. Potency testing of swine erysipelas vaccines by serology - results of a pre-validation study. ALTEX 1999;16:123-8), we initiated an international collaborative study with five European manufacturers and seven regulatory authorities to validate the assay and model. All participants were provided with blind-coded erysipelas vaccines of different potencies, the ELISA kit and test instructions. The participants had to immunise mice, to prepare serum samples and to perform the ELISA. Inter-laboratory reproducibility was reported by the pass/fail criteria of the vaccines under test. Intra-laboratory precision was assessed by comparing repeated measurements on three consecutive days. Day-to-day variation within the laboratories was statistically analysed by comparing pairs of RPs using Lin's concordance correlation coefficient. The results show that the ELISA is indeed a suitable alternative to replace the vaccination-challenge test. Furthermore, this new model reduces the number of animals required for the potency test by approximately 80%.