Potency of 10 BCG vaccines as evaluated by their influence on the bacillemic phase of experimental airborne tuberculosis in guinea-pigs

Abstract

The purpose of this study was to evaluate a low-level aerosol challenge guinea pig model for inclusion in a proposed joint-field-trial laboratory-model assay of the potency of a panel of BCG vaccines. The animal model was one in which guinea pigs were infected via the respiratory route with approximately seven viable virulent tubercle bacilli (strain H37Rv) capable of multiplying and initiating primary lesions. This animal model was used to evaluate the immunizing potency of 10 BCG vaccines. Groups of animals receiving vaccine or placebo were killed 6, 9 or 12 weeks after challenge in order to determine the number of virulent bacilli recoverable from primary-lesion-containing lung lobes and the number recovered from primary-lesion-free lung lobes. Since all lung lobes of each animal were cultured, the percent lobes yielding tubercle bacilli on culture could also be calculated. By these several criteria, each of which evaluates modulation of the bacillemic phase of the infection, all 100 vaccines induced a protective response. One vaccine, an experimental vaccine not used in humans, was of low potency. The remaining vaccines were of moderate to high potency. The results of this study indicate that the low-aerosol-challenge guinea pig model fulfils the criteria for inclusion in the joint-field-trial laboratory-model assay of the potency of BCG vaccines.