The only available vaccine against Mycobacterium tuberculosis, the bacille Calmette-Guérin (BCG) vaccine, is at present being used as a reference for the efficacy of novel vaccines. Herein, we demonstrate that viable BCG can be detected at late time points after vaccination in C57BL/6J mice. If BCG is cleared by antibiotic treatment, the number of mycobacteria-reactive effector cells in the spleen gradually reverts to low levels and consequently immunity in this organ wanes, while resistance in the lung remains stable. The implications for comparing BCG vaccination with experimental vaccines including non-replicating vaccines are discussed.