BCG vaccine extensively used even in countries where efficacy against pulmonary tuberculosis is negligible. A number of possible reasons for the variable efficacy of BCG in different countries have been proposed. None have been proven, some have been disproved, and none can explain the lack of efficacy in both low-TB burden countries (US) and high-TB burden countries (India). The reasons for variable efficacy have been discussed at length in a WHO document on BCG. BCG has protective effects against some non-tuberculosis mycobacteria. BCG has been one of the most successful immunotherapies. BCG vaccine has been the "standard of care for patients with
BCG vaccine 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 effective and safe medicines needed in a 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