A BCG vaccine is given to prevent tuberculosis (TB) infection. The vaccine contains bacteria called BCG (bacille Calmette-Guérin) that is closely related to the bacteria that cause TB.

The BCG vaccine is often given to people in countries where TB is common, such as South America, Africa, Asia, Eastern Europe, and Russia. But it is seldom used in the United States because:

• TB is not a widespread problem in the U.S.
• The effectiveness of the vaccine varies. It is most effective at preventing TB from spreading outside of the lungs (extrapulmonary TB) in children.
• The vaccine interferes with TB skin test results. People who get a BCG vaccination are likely to have TB skin test results that show they have a TB infection even when they aren't infected.