Tuberculosis (TB) vaccine
The Tuberculosis (TB) vaccine, also known as the Bacille Calmette-Guérin (BCG) vaccine, is a weakened strain of the bacteria Mycobacterium bovis, developed in the early 20th century to prevent TB, an infectious disease affecting both humans and animals. First utilized in 1921 after extensive research, the vaccine is administered via injection into the skin, although it can lead to localized reactions and, in rare cases, more serious side effects, particularly in immunocompromised individuals. While BCG is effective in protecting children from severe forms of TB, such as tuberculous meningitis, its efficacy in preventing pulmonary TB among adults is less consistent, with studies suggesting protection lasting anywhere from ten to sixty years.
In regions with low TB prevalence, like the United States, BCG is generally not recommended due to its variable effectiveness and potential interference with TB skin tests. However, targeted recommendations exist for certain populations, including at-risk children and healthcare workers. Ongoing research aims to develop more effective TB vaccines, especially in light of increasing drug-resistant TB strains and the global burden of the disease, which affects approximately one-third of the world's population. Despite its limitations, BCG remains a crucial public health tool, with over four billion individuals vaccinated worldwide.
Tuberculosis (TB) vaccine
ALSO KNOWN AS: Bacille Calmette-Guérin vaccine, BCG
Definition
The tuberculosis (TB) vaccine is a weakened strain of live bacteria that infect cattle. Albert Calmette and Camille Guérin developed the vaccine to prevent TB, an infectious disease of humans and animals caused by various strains of bacteria of the genus Mycobacterium. The weakened strain (M. bovis) was obtained by repeated growth in ox bile media until a strain was produced that would not kill experimental animals or revert to an infectious state. The vaccine, also known as BCG (for its developers), was first used as a vaccine in 1921 after thirteen years of development.
Vaccine Administration
BCG is administered through the skin by injection. Localized skin reactions can occur after vaccination. If drainage occurs, the wound must be covered to prevent transmission of the weakened live bacteria. Serious side effects may include bone infection and disseminated disease, especially in persons who have compromised immune systems. Swelling of the lymph nodes may also occur, and side effects and reactions may appear weeks or months after the vaccine is administered.
Vaccine Efficacy
Studies have shown that BCG protects against tuberculous meningitis and miliary (disseminated) TB in children, but that it provides inadequate prevention against pulmonary TB in adults. These variable outcomes may have been influenced by study designs, geographical location, and statistical factors. Studies also conflict on the duration of protection, ranging from ten to fifteen years to fifty to sixty years.
Several factors may influence vaccine efficacy, including the immune status of vaccinated persons. For example, although persons exposed to Mycobacterium that is endemic to their environment have some inherent protection against Mycobacterium infections, their immune response to BCG is not as pronounced as in persons who have not been exposed to Mycobacterium, such as newborns, infants, and those who live in non-endemic areas. Despite these limitations, BCG remains a vital public health tool, although clinical research is underway to develop a more consistent and longer-lasting TB vaccine.
Official Recommendations
BCG is not generally recommended in the United States because of the low prevalence of TB and because of the variable vaccine efficacy and interference of BCG with the tuberculin skin test (TST). Selective use of BCG is recommended in some persons, such as children, with negative TST and who are continually exposed to either adults with untreated TB or persons infected by strains resistant to isoniazid and rifampin. Healthcare workers should be considered for BCG vaccination in specific situations.
BCG vaccination should not be given to immunocompromised persons, such as those with cancer, those with viral infections such as human immunodeficiency virus (HIV), and those taking medications (such as steroids) that cause immune suppression. Pregnant women should not be vaccinated because of the presence of live bacteria in the vaccine.
Future Vaccines
Several TB vaccines are under investigation because of the appearance of drug-resistant strains, the threat of TB in immunocompromised persons, the easy spread of the disease through the air, and the increasing number of infections relative to population growth. These newer vaccines include genetically modified BCG strains, M. tuberculosis mutants, M. tuberculosis antigens introduced by viruses, and substances in vaccine modifiers (adjuvants). Although not yet available, the M72/AS01E vaccine has shown promise in clinical trials, increasing protection against TB in adults. The emergence of drug-resistant strains has increased investment in newer TB vaccines in the twenty-first century. There has also been increased focus on prevention methods.
Impact
The BCG vaccine is the most commonly used vaccine globally; more than four billion people have been immunized. Over 100 million babies receive the BCG vaccine annually. The vaccine confers protection, though with variable efficacy, against different manifestations of tuberculosis. A more effective vaccine against TB is needed, as it is a contagious disease that infects 1.6 billion people, approximately one-third of the world’s population.
Bibliography
Aronson, N. E., et al. "Long-Term Efficacy of BCG Vaccine in American Indians and Alaska Natives: A Sixty-Year Follow-up Study." Journal of the American Medical Association, vol. 291, 2004, pp. 2086-2091.
"Bacille Calmette-Guérin (BCG) Vaccine for Tuberculosis." CDC, 8 July 2024, www.cdc.gov/tb/hcp/vaccines/index.html. Accessed 2 Oct. 2024.
Dockrell, Hazel M., and Ying Zhang. "A Courageous Step Down the Road Toward a New Tuberculosis Vaccine." American Journal of Respiratory and Critical Care Medicine, vol. 179, 2009, pp. 628-629.
"Global Tuberculosis Programme." Global Tuberculosis Programme, www.who.int/teams/global-tuberculosis-programme/research-innovation/vaccines. Accessed 2 Oct. 2024.
Hoft, D. F. "Tuberculosis Vaccine Development: Goals, Immunological Design, and Evaluation." The Lancet, vol. 372, 2008, pp. 164-175.
West, John B. Pulmonary Pathophysiology: The Essentials. 7th ed., Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins, 2008.