TB doesn’t have an adult vaccine yet. Why not
Tuberculosis (TB) remains the leading infectious cause of death in the world, including India. According to the Global TB Report 2024, an estimated 10.8 million people fell ill with TB in 2023 and 1.25 million died. India accounted for 26 per cent of the world’s cases and an equal percentage of global TB deaths in 2023 — the highest for any country.
In 2015, 194 countries adopted the WHO End TB Strategy, committing themselves to end the disease by 2030 as part of the United Nations Sustainable Development Goals (SDGs). India set 2025 as the target year for TB elimination —five years ahead of the global target of 2030. The End TB strategy aims to achieve the targets of 80 per cent reduction in TB incidence rate and 90 per cent reduction in the number of TB deaths vis a vis 2015.
Despite a very high level of political commitment and increased financial resources over the past few years, the progress in TB control has globally remained rather slow. With only a year to go, India, too, will surely miss its 2025 target of TB elimination.
There are several possible reasons for this slow progress. Most important among them is the advent of the Covid-19 pandemic, which led to widespread disruptions in healthcare, including TB drug supplies and redirection of human resources to address the pandemic.
This severely hampered active TB case detection, diagnosis and treatment, thereby reversing the gains made in the recent past. The global deaths due to TB in 2021 increased for the first time after experiencing a decline for many years.
The treatment of TB takes six months. But adherence to regular intake of medicine over such a long duration often becomes challenging for many patients.
Also, TB comes in different forms — latent infection (which may remain dormant for years), subclinical and clinical TB. Each of these forms requires different tests to diagnose. Many patients latently infected with TB are, in fact, unaware that they have the disease as they may not exhibit the TB symptoms.
Drug resistance, too, is an alarming obstacle to TB prevention and cure, making the treatment harder, expensive and longer to complete. Treatment of multidrug-resistant TB (MDR-TB) is complicated and takes up to two years.
Plus, interaction between TB and HIV is a challenge to public health as HIV infection can complicate the management of TB in many ways. HIV-associated TB often presents as extra-pulmonary disease and sputum-negative. Thus, diagnosis by sputum examination becomes difficult. The TB-HIV interaction increases the rate of drug resistance and enhances the risk of complications. These factors make the fight against TB more challenging.
The most critical issue, however, is the lack of an effective adult vaccine. It has for long been a critical hindrance in the fight against TB. The only licensed vaccine presently available is the Bacille Calmette Guerin (BCG) vaccine. It does prevent severe infection among children, but its efficacy against pulmonary TB in adults is limited.
As of January 2024, there were only 17 TB vaccine candidates listed in the active clinical trial pipeline. This is in stark contrast to the rapid and extensive development of vaccines seen during the Covid-19 pandemic, which took less than a year to develop and be used as an effective public health intervention.
Thus, the target of TB elimination cannot be achieved without substantial technological breakthroughs and their wide application in government programmes.
Top priorities for research and innovation include the development of rapid point-of-care tests for diagnosing TB. Among them are rapid molecular tests which are highly accurate and faster than traditional/conventional microbiological tests. These improved tests can be performed near the patient or in the community-based health centres. They provide quick results, thereby helping in timely treatment. These tests should detect TB and resistance simultaneously.
Addressing the important and substantial problem of ‘missing’ cases or the patients hidden in the community requires innovative approaches to reaching them with diagnosis and treatment. Such cases have the potential to infect others in the community.
Besides active case-finding, population-based mass screening to detect those suffering from TB must be actively explored. Screening should be targeted at high-risk groups, such as the elderly, prison inmates and those with HIV infection, to get a higher yield.
Early detection of TB and swift initiation of treatment can greatly reduce the burden of the disease, risk of poor treatment outcome and adverse socio-economic consequences.
The development of shorter and safer treatment regimens for treating TB infection and TB disease, especially drug-resistant TB, is an important clinical research priority. India has recently approved a new shorter and more efficacious treatment regimen for MDR-TB. It can cure TB in six months as compared to the traditional methods, which take up to two years and have severe side effects.
New TB vaccines could accelerate disease elimination by breaking the cycle of its transmission, improving health equity and reducing the cost of treatment. What is urgently needed is a vaccine that is effective before and after TB exposure, and in all age groups. With many candidate vaccines presently in the pipeline, the possibility of a new vaccine in the near future looks brighter. This endeavour must be supported, encouraged and suitably financed.
Greater emphasis needs to be placed on more effective infection prevention and control activities; stronger surveillance to detect new cases, especially those with drug-resistant TB; community engagement in case detection and compliance with treatment and nutrition; and, finally, greater programmatic outreach for vulnerable populations as part of the universal health coverage.
There is real hope that development and wider application of these tools and innovative mechanisms can accelerate TB elimination in developing countries like India, which carries the highest TB burden in the world.
