The effects of reductions in the numbers of animals used for the potency assay of the diphtheria and tetanus components of adsorbed vaccines by the methods of the European pharmacopoeia.

Forty eight assays of adsorbed diphtheria vaccine and seven assays of adsorbed tetanus vaccine using either a lethal challenge (38 assays) or a serum neutralization test (17 assays) were evaluated for the effects of reductions in the number of animals used at each dilution on the potency values and 95% confidence intervals. The results were assessed in the light of the requirements of the European Pharmacopoeia and the WHO. In the majority of assays, 50% of the number of animals presently required would have sufficed for the determination of a potency within the limits of confidence stipulated by the European Pharmacopoeia and the WHO. Therefore it is concluded that a simplified assay with a reduced number of animals is suitable for the routine potency testing of the diphtheria and tetanus components of the combined vaccines and the monovalent that were examined. Flexibility in the national and international requirements in respect of the numbers of animals used at each dilution is suggested for the routine potency assay of the diphtheria and tetanus components of adsorbed vaccines.