Tuberculosis (TB) is a potentially serious infectious disease that mainly affects the lungs. It is caused by Mycobacterium tuberculosis and usually spreads through the air when someone with TB of the lungs or throat coughs, sneezes, or talks. According to the World Health Organization, it is one of the top 10 causes of death worldwide and the leading cause of death for people with HIV. In 2019 alone, an estimated 10 million people developed active TB disease and 1.4 million died from the disease. Despite being preventable and curable, TB continues to be a major global health problem.
The Bacillus Calmette–Guérin (BCG) Vaccine
The only Tuberculosis Vaccine available for TB prevention is the Bacillus Calmette–Guérin (BCG) vaccine. It was developed in the early 20th century and was the first vaccine developed against a human disease. The BCG vaccine contains a weakened (live but non-pathogenic) strain of the bacterium that causes TB, called Mycobacterium bovis. It is given as a single dose injection, usually into the upper arm muscle. After administration, it stimulates the immune system to develop a type of immunity against TB.
Effectiveness of the Tuberculosis Vaccine
Numerous clinical trials and meta-analyses have concluded that BCG vaccination reduces the risk of severe forms of TB like TB meningitis or miliary TB in children by approximately 50-80%. However, its effectiveness against pulmonary TB, the most common form of TB in adults, is estimated to range from 0 to 80% depending on the region and study. Its efficacy seems to decrease over time after vaccination, usually providing protection for 15-20 years on average. A variety of factors are believed to influence the heterogeneity in BCG efficacy, including environmental mycobacterial exposure, comorbidities like HIV/AIDS, and genetic differences.
Ongoing Research Efforts
Several research initiatives are underway to address the limitations of the current tuberculosis vaccine and develop more effective TB vaccine candidates. Auranofin, an FDA-approved anti-arthritis drug, shows promise as a booster for the BCG vaccine. It helps the BCG vaccine stimulate T cells better. Phase 1 clinical trials involving auranofin are encouraging. Other approaches involve developing genetically engineered BCG strains to enhance immunogenicity, viral-vectored delivery systems, and subunit vaccines focusing on specific M. tuberculosis antigens. Theravax, a Swiss biotech company, is developing a BCG vaccine coded with a viral tuberculosis antigen to provide longer-lasting protection.
Improving Tuberculosis Vaccine Delivery Strategies
In addition to new vaccine candidates, enhancing BCG vaccination programs could reduce the global burden of TB. Current WHO recommendations are for BCG vaccination at birth or soon after in high-burden countries. However, late or inadequate BCG vaccination coverage remains a challenge in certain regions and risk groups. Alternative strategies are being explored, such as using the skin-patch technique to deliver BCG instead of traditional intradermal injection, improving cold-chain management during transport and storage, and developing thermostable BCG freeze-dried powder formulations. BCG revaccination of adolescents and high-risk adults is also being evaluated as an approach to boost waning immunity.
While the tuberculosis vaccine provides partial protection against severe forms of childhood TB, it does not replace the need for new and improved vaccines with higher efficacy levels, especially against pulmonary TB in adults. Multiple promising candidate vaccines are currently in clinical testing phases. In addition, strategies to enhance implementation and delivery of the current BCG program can help fill critical gaps. Achieving global TB eradication will likely require a combination approach utilizing both new vaccines as well as public health interventions to curb remaining transmission. Improved diagnostics and anti-tuberculosis treatments that are faster-acting, shorter in duration, and affordable are also critical tools in the overall response against this age-old yet ongoing health threat.
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