Is the TB Test a Live Vaccination?

According to the Centers for Disease Control and Prevention, more than 9 million new cases of tuberculosis worldwide are diagnosed each year. The PPD (short for purified protein derivative) skin test for TB is a valuable diagnostic tool for preventing transmission and starting proper treatment.

Tuberculosis

• Tuberculosis is a bacterial infection that mostly affects the lungs. Most cases are in underdeveloped countries, but there were about 13,000 in the United States in 2008.

Vaccines in General

• Vaccines are made from dead or attenuated viruses, and from bacteria that are unable to cause disease. They cause an immune reaction that confers immunity to future infections by viruses or bacteria similar to those in the vaccine.

TB Skin Test

• The TB skin test does not qualify as a vaccine. It does not contain the whole TB bacteria. Instead, it contains the bacteria's proteins. The proteins are injected under the skin of the forearm, and then the skin is observed for a reaction.

Positive Test

• If a person is infected with TB or has been exposed to it, her immune system will make antibodies against the bacteria. When the protein is injected under the skin, the antibodies trigger a localized immune response, causing a hard, red bump to form at the site of the test.

TB Vaccine

• There is no vaccine against TB in use in the United States. Other countries use a vaccine called bacillus Calmette-Guerin, which is a bacterium similar to the one that causes TB. In the United States, screening with the test and administering antibiotics is preferred to vaccination.