A vaccine used to prevent tuberculosis (TB) in people who are at a high risk of TB or where TB is common. It is rarely given in the U.S. It is made from a weakened form of a bacterium called Mycobacterium bovis (bacillus Calmette-Guérin), which is similar to the bacteria that cause TB. The vaccine may help the body’s immune system make antibodies to destroy the TB bacteria. It also may help the immune system kill cancer cells and is being studied in the treatment of melanoma.