As per the World Health Organization, tuberculosis tops the list of the cause of infectious disease-related deaths worldwide. This alarming statistic underscores the urgent need to devise a comprehensive strategy for the global eradication of tuberculosis. In the realm of infectious diseases, vaccines often stand as our most potent tool for achieving such a goal. However, when it comes to tuberculosis, a unique set of challenges emerges. This blog delves into the advancements and formidable obstacles confronting the medical research and healthcare community in their relentless pursuit of a successful tuberculosis vaccine.
The End TB Strategy by WHO
The World Health Organization recognizes tuberculosis as a major health threat and has hence developed the end-TB strategy. The goal of this strategy, as the name suggests, is to make the world completely immune to the disease. In this context, it aims at a 90% reduction in TB incidence and 95% reduction in TB mortalities by the year 2035. However, in order to succeed in this goal, we need to develop an effective vaccine against the disease, as vaccination is so far the most efficient strategy to stop the spread of an infectious disease.
The Current Status of TB Vaccination
The Bacillus Calmette-Guérin (BCG) vaccine, developed in the early 20th century, is the only licensed vaccine for TB. While BCG provides some protection against severe forms of TB in children, its effectiveness in preventing pulmonary TB in adults is limited. This has prompted a renewed focus on TB vaccine research, leading to the development of novel candidates in recent years.
A vaccine technology that shows promise in preclinical studies is the CMV (cytomegalovirus) vector. Engineering on this live, attenuated and persistent viral vector has shown low-level replication of the MTB virus. Hence, this technology offers long-term immunity in eradicating TB.
Progress in TB Vaccine Research
Here are some key progress indicators in the development of an effective TB vaccine:
Subunit Vaccines
Researchers are looking towards subunit vaccines that target specific antigens of the tuberculosis bacterium, Mycobacterium tuberculosis. These antigens elicit an immune response that more specifically targets the infection. M72/AS01E and H56:IC31 are two promising candidates that have shown promise in early-stage clinical trials.
Viral Vector Vaccines
Another strategy involves employing harmless viruses to convey TB antigens into the body. Among the viral vectors being investigated are adenoviruses and modified vaccinia Ankara (MVA). These vaccinations are designed to trigger a powerful and long-lasting immunological response when combined with the older BCG vaccine.
Whole Cell-Based Vaccines
Recombinant BCG strains are being developed to enhance the immune response generated by the original BCG vaccine. According to studies, these modified BCG vaccines, such as VPM1002 and rBCG30, aim to provide better and longer-lasting protection.
Challenges in the development of TB Vaccine
- Complexity of the bacteria
The TB bacterium, Mycobacterium tuberculosis is a complex bacterium that has multiple strains and antigens. This makes it difficult to develop a vaccine that eliminates all the strains effectively while also exhibiting a strong immune response in the body.
- Limited biomarkers
Another key challenge in developing a TB vaccine is the lack of clear biomarkers that can aid in evaluating the effectiveness of vaccine candidates.
- Technical difficulties
Among other challenges include the technical obstacles such as the long research duration needed to develop an effective solution, the high cost and technological tools needed for the same as well as the regulatory considerations that go into conducting clinical trials for the vaccine.
Key Takeaways
In a nutshell, developing an effective vaccine for TB is still a work-in-progress. However, considering the multiple roadblocks on the way and the promising progress that health organizations worldwide have made till date, we have a reason for hope. By responsibly joining hands as a community, each of us can contribute towards the end-TB strategy of WHO.
References:
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5850090/#:~:text=We%20have%20made%20substantial%20progress,TB%20vaccines%20for%20further%20development.
- https://www.who.int/publications/i/item/WHO-HTM-TB-2015.19
- https://globaltb.njms.rutgers.edu/educationalmaterials/calendar/2022/TB%20Vaccines_Schrager%20.pdf
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5850090/#:~:text=We%20have%20made%20substantial%20progress,TB%20vaccines%20for%20further%20development.
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9263712/
- https://en.wikipedia.org/wiki/MVA85A#:~:text=MVA85A%20(modified%20vaccinia%20Ankara%2085A,the%20older%20TB%20vaccine%20BCG.
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8648981/