Potency tests of diphtheria, tetanus and combined vaccines. Suggestion for a simplified potency assay

Two diphtheria-tetanus vaccines (DT), adsorbed to either aluminium hydroxide or calcium phosphate but identical with respect to toxoid origin and amounts, were compared in full potency assays in mice according to the European Pharmacopoeia (EP) and in a reduced potency assay in guinea-pigs using a double dose immunization schedule. The efficacy of the vaccines was compared in a clinical trial with revaccination of 313 military recruits. The reduced potency assay gave a better reflection of the efficacy of the two vaccines in humans than the required assays of the EP. For release of combined, final vaccine formulations the reduced potency assay suggested will reduce the number of animals in quality control.