Back in 1882, when German microbiologist Robert Koch discovered the microbial causes of tuberculosis, researchers thought that the disease could be defeated with vaccines and drugs. But in the mid-1980s, a tuberculosis epidemic rampaged across the world, killing millions. Soon it got the tag of a global pandemic. As per the WHO Global Tuberculosis Report 2019, India has the highest number of patients suffering from tuberculosis in the world. Though the Ministry of Health and Family Welfare’s National Strategic Plan (NSP) for tuberculosis elimination is aimed at wiping off the epidemic by 2025, researchers say that five years is a short period to accomplish this. The question of whether it is possible for a vaccine to give complete protection against the TB or prevent its development has perplexed researchers for over 20 years now.
Currently, the only licensed vaccine against TB is a live but crippled strain of a pathogen (Mycobacterium bovis) which is similar to the bacterium that causes TB (Mycobacterium tuberculosis). The strain, bacilli Calmette-Guérin (BCG), which is given at birth or early in life, has been around for about 100 years. It is definitely effective when it comes to preventing certain types of TB in children but in the case of adolescents and adults, the pathogen often resists the immune responses elicited by vaccination. Surprisingly, most people who die from TB were administered BCG as a child. But the problem is not with the strain used in the vaccination, rather the way it is administered. According to a recent study by Robert Seder and his team at the National Institute of Allergy and Infectious diseases in Maryland, a near-complete protection from TB infection can be had using the century-old vaccine by changing its route of administration. Usually, the vaccine is intradermal—injected into the skin. But it turns out to be super effective when it is delivered directly to a vein.
The studies done on monkeys showed that delivering the vaccine via veins rather than the skin can dramatically increase its potency. Robert had earlier discovered that delivering a malaria vaccine directly into the bloodstream, through a vein, was much more effective that delivery through skin or muscle. This raised the question whether a similar route of delivery of BCG vaccine would work for TB. The study was done on monkeys wherein one group (10 monkeys) was vaccinated with BCG by injecting the vaccine under the skin (the usual route) and the other was administered the vaccine intravenously. Months later, the monkeys were exposed to M. tuberculosis. Only two out of the ten monkeys that received the vaccine into the skin were protected from the infection whereas nine out of ten monkeys that had the vaccine intravenously were protected. Monkeys given the vaccine via veins also showed much higher levels of T-cells in the lungs—a key part of the immune system’s protection against TB. The T-cells which can recognise and kill the bacteria, increased 100-fold in the lungs. The lungs of the monkeys in the second group were free of any form of infection. The success of BCG IV will bring hope to millions across the globe who are battling TB. Although the tests in humans can be around 18 months off, the vision for 2025—elimination of TB—could still be a possibility.