Caused by the bacterium Mycobacterium tuberculosis, tuberculosis can be present in a latent or active form. The latent form is dormant and causes no symptoms. The active form, however, can be deadly. The bacille Calmette-Guerin vaccine, or BCG, has long been the standard vaccine for tuberculosis. BCG is widely used in countries where tuberculosis is prevalent and is occasionally used in the United States in populations with a high incidence of the disease.
History
The bacille Calmette-Guerin vaccine was developed in Paris in 1921 from a strain of mycobacterium that was similar to Mycobacterium tuberculosis but affected cows instead of people. Over time, the vaccine underwent mutations in the various places where it was cultured, creating substrains, or subcultures, of BCG.
Problems
Because of mutation in the various substrains of BCG over time, the vaccine has become less effective against some forms of tuberculosis. When first isolated, it was about 80 percent effective against pulmonary tuberculosis, which infects the lungs, explains Science Daily. Now it is almost completely ineffective against this form of tuberculosis.
Benefits
The BCG vaccine is still about 80 percent effective against military tuberculosis, or disseminated tuberculosis, a type of tuberculosis affecting all of the body. Military tuberculosis is more prevalent in children under 5, according to the Children's Hospital of Philadelphia. Because tuberculosis affects about a third of the worldwide population, the vaccine can still help prevent deadly infection in infants and small children, saving lives.
Recommendations
In the United States, vaccination with BCG is not widely recommended, since childhood disseminated tuberculosis is rare in developed countries. The Centers for Disease Control and Prevention recommends the vaccine only for children who are in close contact with adults who have tested positive for tuberculosis and for adults who work with populations in which there is a high rate of tuberculosis.
Contraindications
Individuals whose immune systems are compromised should not receive the tuberculosis vaccine. The CDC also advises pregnant women to avoid the vaccine, since studies have not determined its safety during pregnancy.
Potential
Research into why the BCG vaccine has become less effective against pulmonary tuberculosis is under way as scientists seek to restore the vaccine's potency. Other researchers are investigating new, more effective vaccines for tuberculosis. As of 2010, some of these have reached the clinical trial stage, including the MVA85A vaccine, developed in Britain.
