When people refer to a “TB shot,” they often mean either a test for tuberculosis infection or, less commonly, a vaccine. The term can cause confusion about what these procedures involve and when they are necessary. This article clarifies the distinctions between tuberculosis testing and vaccination, guiding on situations where screening or immunization might be recommended. Understanding these differences helps navigate health recommendations.
Understanding the “TB Shot”: Vaccine vs. Test
The term “TB shot” can refer to two distinct procedures: diagnostic tests for tuberculosis infection or the actual vaccine. The tuberculin skin test (TST), often called the Mantoux test, is a common diagnostic tool. This test involves injecting a small amount of fluid, called tuberculin, just under the skin, typically on the forearm. A healthcare worker then checks the injection site 48 to 72 hours later for a reaction, which determines if there has been exposure to TB bacteria.
Another diagnostic option for detecting TB infection is the TB blood test, also known as an Interferon-Gamma Release Assay (IGRA). These blood tests are preferred because they require only one visit, are more accurate, and are not affected by prior BCG vaccination, which can cause false positive results with the TST. Both the TST and IGRA identify if a person has been infected with TB bacteria, indicating latent TB infection or active TB disease.
The actual TB vaccine is Bacillus Calmette-Guérin (BCG). This vaccine is not routinely recommended in countries with a low incidence of tuberculosis, such as the United States. Reasons include the low risk of TB infection, variable effectiveness against adult pulmonary TB, and potential interference with tuberculin skin test results. However, BCG is widely used in countries with a high prevalence of TB, primarily to protect infants and young children from severe forms of the disease, like TB meningitis.
When and Why You Need TB Testing or Vaccination
Routine, widespread TB testing for the general population without specific risk factors is not a common practice in the United States. Instead, testing frequency is determined by an individual’s potential exposure and risk factors for tuberculosis infection or progression to active disease. This risk-based approach helps target screening efforts to those who will benefit most from early detection.
Certain groups require regular TB testing due to increased risk of exposure or developing active disease. Healthcare personnel are screened for TB upon hire. Routine serial testing for healthcare workers, such as annually, is not recommended unless there has been a known exposure or ongoing transmission within a healthcare facility. Annual TB education, covering risk factors and symptoms, is important for these individuals.
Individuals who have been in close contact with someone diagnosed with active TB disease should undergo testing. Testing is recommended immediately and again 8 to 10 weeks after the last known exposure to ensure accurate detection, as the body needs time to develop a detectable immune response. People with weakened immune systems (e.g., those with HIV, organ transplant recipients, or on immunosuppressive medications) are at higher risk of TB infection progressing to active disease and may require specific testing protocols.
Testing is performed for individuals in several situations:
Born in or frequently traveling to high-TB prevalence countries (e.g., Asia, Africa, Latin America).
Undergoing U.S. immigration processes (primarily for active TB disease).
Living or working in congregate settings (e.g., correctional facilities, homeless shelters, nursing homes).
Developing symptoms suggestive of TB (e.g., persistent cough, chest pain, unexplained weight loss, fever, night sweats).
Regarding BCG vaccination, it is administered as a single dose in infancy or early childhood in countries where it is part of the immunization schedule. Booster doses of the BCG vaccine are not recommended by the World Health Organization.
The Importance of TB Screening and Prevention
Tuberculosis screening and prevention efforts are important for public health. Screening for TB helps identify latent TB infection before it can progress to active disease. Early detection allows for prompt intervention, significantly reducing the risk of infection advancing to a contagious and symptomatic state.
Treating latent TB infection is an effective strategy for preventing the development of active, contagious tuberculosis. Approximately 5% to 10% of people with untreated latent TB infection will develop active TB disease over their lifetime. By identifying and treating individuals with latent infection, the chain of transmission within communities is broken, protecting vulnerable populations from exposure. This proactive approach contributes to controlling the spread of tuberculosis and working towards its elimination.