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Protective efficacy of the different vaccine strains against low-dose pulmonary challenge in guinea pigs. Nine weeks postvaccination, guinea pigs were infected via the aerosol route with 5 to 10 viable M. tuberculosis organisms. Five weeks later, these animals were euthanized and the the number of CFU of M. tuberculosis was evaluated in the lung (A) and the spleen (B). The CFU-per-organ values indicated are the geometric means + SEM; n is the number of animals used.
