Bacille Calmette Guerin (BCG) is the most widely used vaccination in the world. BCG is made of a live, weakened strain of Mycobacterium bovis, (a cousin of Mycobacterium tuberculosis, the TB bacteria). It was developed in the 1930's and it remains the only vaccination available against tuberculosis today. It is used because it is effective in reducing the likelihood and severity of TB in infants and young children. That is especially important in areas of the world where TB is highly prevalent, and the chances of an infant or young child becoming exposed to an infectious case are high.
In countries with high rates of TB, BCG is often given to infants at the time of birth because it helps prevent the more serious forms of TB disease from developing in children. Unfortunately, the positive effect of BCG in protecting infants and young children from endemic areas from the lethal forms of TB does not extend to the adult years. Thus, many people develop active tuberculosis even though they received BCG, even in multiple doses, in earlier years.
