Tuberculosis and the microbe that causes it, Mycobacterium tuberculosis, have dogged humanity down the millennia. This ancient plague continues to blight human lives, leading to almost nine million new cases and causing 1.4 million deaths globally each year. India shoulders the highest burden of TB in the world and some three lakh people could die of the disease this year. In recent times, there have been determined efforts to develop new and more effective vaccines that could curb this disease and thereby reduce human suffering and deaths. The only vaccine available at present, ‘bacille Calmette-Guérin’ (BCG), can protect infants and young children. But it has often not stopped infected adolescents and adults from developing active forms of the disease. Moreover, as BCG uses a live but greatly weakened version of a closely related bacterium, the vaccine has been found to be unsafe for babies infected with the Human Immunodeficiency Virus (HIV). There are already about a dozen TB vaccines that are in various stages of clinical trials and more are in the pipeline. The current vaccine candidates are not intended to block infection right at the outset or mobilise the body’s defences to completely eliminate bacteria that have gained entry. Rather, the hope is that these vaccines can help prevent active TB, thus reducing sickness and death as well as limiting spread of the disease. In more than 90 per cent of those infected, the immune system is able to contain the bacterium and hold it in a latent state. How such protective immunity works is not fully understood, and the vaccines currently being tested could well fail to replicate it. As one review paper published in a journal earlier this year observed, “there is no guarantee that these vaccines will be significantly superior to … BCG.”

A vaccine that was originally developed at the National Institute of Immunology in Delhi against leprosy has completed the final stage of clinical trials to see if it can aid the treatment of those with tuberculosis. The vaccine uses a heat-killed bacterium, Mycobacterium w. Tests carried out in mice showed that it could be a useful adjunct to chemotherapy. The results of the latest clinical trials have not yet been released. But if in humans too the vaccine produces an enhanced immune response, it might be able to reduce the duration of chemotherapy that sufferers with active TB have to undergo and also allow better cure rates to be achieved. As with HIV, developing truly effective vaccines against tuberculosis could well be a long drawn-out process. Failures will occur, but the quest for better vaccines must not falter.

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