The Bacillus Calmette-Guerin (BCG) vaccine was first used medically in 1921. Since then it has remained the primary and only vaccine for tuberculosis worldwide, with more than a hundred million kids being vaccinated every year as of 2004. It features on the WHO’s List of Essential Medicines, and in countries where TB is common, such as India, every child is given the vaccine soon after birth.
Co-developed by the French physician and biologist Albert Calmette and immunologist Camille Guerin, the BCG vaccine uses a bacteria called Mycobacterium Bovis. The bacteria are attenuated, meaning it is weakened to a point where it cannot cause infection anymore, but can still trigger an immune response.
Once this happens, the immune cells of the body can “remember” the bacteria and prevent further attacks. There are specific proteins on a bacterial cell that cause this immune response, called antigens. Mycobacterium Bovis was chosen because its antigens are similar to Mycobacterium tuberculosis, which causes tuberculosis. Other than tuberculosis, the BCG vaccine also prevents leprosy and Buruli ulcers and is also used in immunotherapy for bladder cancer.
However, the BCG vaccine has its limitations. It protects primarily children, who are more likely to suffer from serious disease if they are infected but is not an adult vaccine, where adults are the ones mostly affected by the disease.
Even in children, it prevents infection in only 20% of those vaccinated, while among the rest, it prevents serious disease in half of them if they get TB. This efficacy further varies widely across regions and countries. Also, the BCG vaccine mainly acts to prevent tuberculosis of the brain, while the most common form of tuberculosis in India and elsewhere is tuberculosis of the lungs.
This shows an immediate need for a better vaccine or a vaccine that gives protection to a wider group of people. Yet for a hundred years no new vaccine has emerged. This can be attributed to the fact that tuberculosis is seen in the poorest nations and the poorest areas of these nations. Also, in India, there is a social stigma about the disease. It is thus mostly overlooked.
However, the Indian government has pledged to eliminate tuberculosis from the country by 2025 and has undertaken many steps in that direction. One such step is the formation of research consortiums like the India TB Research Consortium or ITRC headed by the Indian Council of Medical Research (ICMR). The aim is to select vaccines that are in development, funding them for trials and having at least one working vaccine co-owned by the government within 2025.
The ICMR has selected two potential vaccine candidates and recruited 12,000 volunteers for further trials. One of the vaccines is Immuvac, which consists of a bacteria called Mycobacterium indicus pranii, and was developed to prevent leprosy. The other is called VPM1002 and is a recombinant form of the BCG vaccine itself. The bacteria in the vaccine have been changed in a way so that they can develop stronger immune protection.
These new vaccines are meant for adults who are in close contact with a person suffering from TB. But due to the chronic nature of the disease, it will take three years of monitoring before vaccines can be approved for public use. Even if these vaccines are successful, they will still cover only a part of the population, as they are meant to be used in specific conditions.
The primary level of defence against tuberculosis in India remains proper diagnosis and treatment. Tests like CBNAAT and TrueNat, which are the benchmark nowadays, must be made available to all healthcare and TB centres. Meanwhile, drugs that can tackle both normal and multidrug-resistant forms of tuberculosis should also be available to all people across the country.