New Delhi: Vaccination will play an important role in eradicating TB. While certain vaccine candidates in advanced stages of clinical trials raise hope for the future availability of new tools, in the immediate term, there is also increasing interest in Bacille Calmette Guerin (BCG) revaccination among adults and adolescents as a potential strategy," the study conducted by Indian Council of Medical Research (ICMR) said.
Currently, the only licensed vaccine against TB is BCG, the live-attenuated vaccine form of Mycobacterium bovis. In use for almost a century, the main benefit of the BCG vaccine is to protect young children from severe forms of TB. There are several TB vaccine candidates currently in development as alternatives, with three for adults and adolescents in phase III trial.
Significantly, India aims at eliminating tuberculosis by 2025, five years ahead of the target set by the UN's sustainable development goal. In 2016, India lost nearly 4,23,000 TB patients-a third of the world's 1.4 million TB death toll. It is worth mentioning that in India 7.9 per cent of the TB-related deaths are caused by tobacco.
"In high-burden settings such as India, vaccination will be critical in bringing down TB incidence and mortality, to meet the end of TB goals. Mathematical modelling offers a helpful tool for anticipating the potential impact of vaccination strategies," the ICMR study said. The study further said that a disease-preventing vaccine would have a stronger impact than an infection-preventing one.
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According to the findings, when rolled out in the general population, an infection-preventing vaccine would avert 12 per cent of cumulative TB incidence between 2023 and 2030, while a disease-preventing vaccine would avert 29 per cent. Although the vulnerable population accounts for only around 16 per cent of India's population, prioritising this group for vaccination would achieve almost half the impact of rollout in the general population, it said. According to the National Prevalence Survey of India (2019-2021), 31 per cent of TB infection burden among individuals above 15 tears of age.
"One key reason for this result could be the slow natural history of TB, specifically with infected individuals typically taking a year or longer to develop active TB. Thus, while an infection-preventing vaccine may take several years to show the effect on active TB amongst those not yet infected, the benefits of a disease-preventing vaccine are more likely to be felt in the short term, particularly among those already infected, who would soon develop the disease," the ICMR study said. Another notable result of the study is the disproportionate impact of prioritising vaccination in the vulnerable population.
"Although this group was assumed to account for only 16 per cent of the general population, targeted vaccination achieves over 40 per cent of the incidence and mortality reductions that could arise from vaccinating the general population," the ICMR study pointed out. The ICMR study highlights that if vaccine coverage needs to be focused on during the initial stages of rollout, it would have a disproportionate impact when prioritised for vulnerable population bearing a high burden of TB.
The premier medical research institute has stated that while vaccines currently in the development pipeline, may take years to be licensed and widely deployed, BCG revaccination can offer a valuable approach in the short term. "Recent studies have shown promising results regarding the immunogenicity and efficacy of BCG revaccination as well," the findings said.
