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What Is a BCG Vaccination?

By Amanda Barnhart
Updated Feb 20, 2024
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A bacille Calmette-Geurin (BCG) vaccination is a tuberculosis vaccine commonly given in countries with high rates of tuberculosis. The vaccination is made from small amounts of live bacteria similar to the bacteria that cause tuberculosis. People who become infected with tuberculosis after receiving a BCG vaccination often get well very quickly because the vaccine prevents the tuberculosis bacteria from spreading in the body.

The BCG vaccination has been used since 1921 and is very effective in controlling tuberculosis. Studies vary, but most research indicates an efficacy between 56 and 80 percent and may be as high as 100 percent when administered to young children. There are different types of the BCG vaccination, which are derived from different strains of the Mycobacterium bovis bacteria.

Children who test negative for tuberculosis and live in areas where they are constantly exposed to tuberculosis should receive the BCG vaccination. This is particularly important for children in areas where isoniazid- and rifampin-resistant tuberculosis is common. Health care workers may need the vaccination if they are continually exposed to tuberculosis and are likely to become infected.

Most individuals do not experience a negative reaction to the BCG vaccine. The most common side effects of the injection include muscle soreness and the formation of small pustules near the injection site. These side effects usually resolve on their own, but they may last several months. Permanent scarring at the injection site is possible. While rare, some people develop an infection several months or years after vaccination that can lead to bone lesions.

Certain people should not get the BCG vaccination due to potential complications. It is not known whether the vaccine could harm a fetus in utero, so pregnant women should not get the vaccine. Since the vaccine carries small amounts of live bacteria, people with lowered immune systems due to HIV or other medical conditions or who recently underwent an organ transplant should not be vaccinated because they could become extremely ill.

People who receive the BCG vaccination may falsely test positive when they receive a tuberculin skin test. This can make it difficult for doctors to determine if the individual is actually infected with tuberculosis or if the reaction to the skin test is from the vaccination. Blood tests for tuberculosis are more accurate in people who have been vaccinated since the vaccine will not cause a false positive on a blood test.

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