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 bladder cancer (NMIBC)" since 1977. By 2014 there were more than eight different considered biosimilar agents or strains used for the treatment of non–muscle-invasive bladder cancer (NMIBC). Except in neonates, a tuberculin skin test should always be done before administering BCG. A reactive tuberculin skin test is a contraindication to BCG. Someone with a positive tuberculin reaction is not given BCG, because the risk of severe local inflammation and scarring is high, not because of the common misconception that tuberculin reactors "are already immune" and therefore do not need BCG. People found to have reactive tuberculin skin tests should be