BCG, or bacille Calmette-Guerin, is a vaccine for TB disease that is used in many countries. However, BCG is not generally recommended in the United States because there is a low risk of infection with M. tuberculosis and because the effectiveness of BCG has varied substantially--from 0% to 76% in eight major studies. In a recent meta-analysis, data from all clinical trials of BCG were combined and analyzed. The protective effect of BCG was found to be 50% against all forms of TB and 64% against TB meningitis.
However, caution must be used in applying the results of this meta-analysis to public health practice. Because BCG varies so widely in effectiveness and because the reasons for this variation are unknown, estimates of its effectiveness in different populations cannot be translated directly to equal protective effects in individuals.
Furthermore, BCG immunization may cause a positive reaction to the tuberculin skin test. Thus, it may complicate decisions about giving preventive therapy to BCG-vaccinated persons who have a positive skin test result.
CDC recommendations for BCG vaccination were most recently published in November 1988. According to these recommendations, BCG vaccine should be given only to infants and children with negative tuberculin skin test results who
These recommendations are currently being revised. Please refer to the latest published recommendations.
BCG is contraindicated in persons who have an impaired immune response (e.g., persons who have HIV infection, leukemia, or lymphoma) or who are immunosuppressed because of steroids, alkylating agents, antimetabolites, or radiation therapy. HIV infection should be ruled out before BCG vaccine is administered to persons in groups at high risk for HIV infection. It is also prudent to avoid giving BCG vaccination to pregnant women, although no harmful effects of BCG on the fetus have been observed.
Many foreign countries still use BCG as part of their TB control programs, especially for infants. In persons vaccinated with BCG, sensitivity to tuberculin is highly variable, depending upon the strain of BCG used and the group vaccinated. There is no reliable method of distinguishing tuberculin reactions caused by BCG from those caused by natural infections.
A reaction to tuberculin in a person with a history of BCG vaccination is more likely to be due to infection with M. tuberculosis if
In a BCG-vaccinated person who has any of the preceding risk factors, a positive tuberculin reaction probably indicates infection with M. tuberculosis. Such persons should be evaluated for isoniazid preventive therapy after disease has been ruled out.