Protection to mice afforded by BCG vaccines against an aerogenic challenge by three mycobacteria of decreasing virulence.

Specific pathogen-free mice were vaccinated subcutaneously with 10(7) CFU of BCG Pasteur or BCG Glaxo and 30 or 90 days later, the mice were challenged aerogenically with Mycobacterium tuberculosis (Erdman or South Indian strains) or with M. avium. Both vaccines induced substantial levels of resistance to tuberculosis and tuberculin hypersensitivity. There was no detectable difference in the host response to the three aerogenic challenges which could be related in any way to the immunogenicity of the BCG strain or to the mouse virulence of the challenge organism. These results do not support the hypothesis that the protective activity of BCG vaccines varies, depending upon the virulence of the infecting organism.