Bacille Calmette-Guerin (BCG) is a live, attenuated (weakened) vaccine derived from a strain of Mycobacterium bovis and used in many countries with a high prevalence of tuberculosis to prevent children from contracting severe disseminated tuberculosis (TB) or TB meningitis. The vaccine was developed over several years by Albert Leon Charles Calmette and Jean Marie Camille Guerin at the Pasteur Institute in Lille, France. An early version of BCG was first administered to humans in 1921. Since then, many different strains have been developed and used throughout the world.

However, the BCG vaccine is not generally recommended in the United States for many reasons, including:

  • The low risk of infection with Mycrobacterium tuberculosis
  • The variable efficacy of the BCG vaccine against pulmonary TB
  • The low risk of severe disseminated TB disease in young children in the United States
  • The vaccine’s interference with the ability to determine Mantoux tuberculin skin test (TST) reactivity

Currently, there are two methods available for the detection of M. tuberculosis infection in the U.S.—TST and interferon-gamma release assays (IGRAs) blood tests, and they are not contraindicated for persons who have been vaccinated with BCG.

BCG vaccination may cause a false positive reaction to the TST, which may complicate decisions about prescribing treatment. The presence or size of a TST reaction in people who have been vaccinated with BCG does not predict whether BCG will provide any protection against TB disease. Furthermore, the size of a TST reaction in a BCG vaccinated person is not a factor in determining whether the reaction is caused by latent TB infection (LTBI) or the prior BCG vaccination. Therefore, TST results in people vaccinated with BCG should be interpreted using the same criteria as for those not BCG vaccinated.

IGRAs (blood tests) unlike the TST, are not affected by prior BCG vaccination and are less likely to give a false positive result.