How does the BCG vaccine provide some protection against tuberculosis?

The BCG vaccine provides protection against tuberculosis by utilizing a weakened, attenuated strain of Mycobacterium bovis, a bacterium closely related to the pathogen that causes the disease.12

When this vaccine is injected into the skin, it triggers a local immune response. This process confers a degree of immunity against infection by M. tuberculosis for several years. While the vaccine is not universally effective, it is particularly successful in protecting infants and young children from serious forms of the disease. Because of its variable efficacy and the potential for it to cause false-positive results on tuberculin skin tests, its use is generally prioritized in countries where the prevalence of tuberculosis remains high.31