Wikipedia
Bacillus Calmette–Guérin (BCG) vaccine is a vaccine primarily used against tuberculosis. In countries where tuberculosis is common one dose is recommended in healthy babies as close to the time of birth as possible. Babies with HIV/AIDS should not be vaccinated. In areas where tuberculosis is not common, only babies at high risk are typically immunized while suspected cases of tuberculosis are individually tested for and treated. Adults who do not have tuberculosis and have not been previously immunized but are frequently exposed to drug resistant tuberculosis may be immunized as well. It is also often used as part of the treatment of bladder cancer.
Rates of protection against tuberculosis infection vary widely and protection lasts between ten and twenty years. Among children it prevents about 20% from getting infected and among those who do get infected it protects half from developing disease. The vaccine is given by injection into the skin. Additional doses are not supported by evidence. It may also be used in the treatment of some types of bladder cancers.
Serious side effects are rare. Often there is redness, swelling, and mild pain at the site of injection. A small ulcer may also form with some scarring after healing. Side effects are more common and potentially more severe in those with poor immune function. It is not safe for use during pregnancy. The vaccine was originally developed from Mycobacterium bovis which is commonly found in cows. While it has been weakened, it is still live.
The BCG vaccine was first used medically in 1921. It is on the World Health Organization's List of Essential Medicines, the most important medication needed in a basic health system. Between 2011 and 2014 the wholesale price was $0.16 to $1.11 USD a dose in the developing world. In the United States it costs $100 to $200 USD. As of 2004 the vaccine is given to about 100 million children per year globally.