BCG vaccine effectiveness in preventing tuberculosis and its interaction with human immunodeficiency virus infection

Background To explore Bacillus Calmette-Guerin vaccine (BCG) as a protective factor against tuberculosis (TB) and how human immunodeficiency virus (HIV) infection modifies the effect of BCG on TB. Methods Two matched case-control studies were conducted. One study compared TB cases and controls who were HIV positive. The second compared TB cases and controls who were HIV negative. The study population consisted of 88 TB cases and 88 controls among HIV-positive individuals and 314 TB cases and 310 controls among HIV-negative individuals. Cases were new TB diagnoses, confirmed by either bacteriology, pathology, radiology or clinical response to treatment; controls were selected from people without TB symptoms and who sought medical attention in the same institution where a case was enrolled. BCG was assessed by the presence of a typical scar. Results The level of protection against all clinical forms of TB was 22% among HIV positive individuals (odds ratio [OR] = 0.78, 95% CI:0.48-1.26) and 26% among HIV negatives (OR = 0.74, 95% CI:0.52-1.05). There was a significant difference (P = 0.002) in the level of protection against extrapulmonary TB (ETB) between HIV-negative (OR = 0.54, 95% CI:0.32-0.93) and HIV-positive individuals (OR = 1.36, 95% CI:0.72-2.57). Conclusion BCG has a modest protective effect against all forms of TB independent of HIV status, and BCG confers protection against extrapulmonary TB among HIV-negative individuals. However, HIV infection seems to abrogate the protective effect of BCG against extrapulmonary TB. Our data support the public health importance of BCG vaccine in the prevention of extrapulmonary TB among immunocompetent individuals.