Tuberculosis is out of control in developing countries, where it is killing millions of people every year. In these areas, the present vaccine — Mycobacterium bovis bacillus Calmette–Guérin (BCG) — is failing. Progressive tuberculosis occurs because the potentially protective T helper 1 (T_H1)-cell response is converted to an immunopathological response that fails to eliminate the bacteria. Here, we discuss the data indicating that the problem in developing countries is not a lack of adequate T_H1-cell responses but, instead, an exaggerated tendency to switch to immunopathological responses. We propose that a successful vaccine needs to block this immunopathology, because it is not the quantity of T_H1-cell activity that matters but, rather, its context.