New York: The world’s only exclusive vaccine against leprosy was developed in India in the early 1970s. But the country continues to report 60 per cent of leprosy cases across the world today.
Also known as Hansen’s disease, leprosy is caused by bacteria called Mycobacterium leprae (M. leprae). It mainly affects the skin and nerves, and can cause deformities and disabilities as long-term consequences, which is why there’s a stigma associated with this disease. The exact mechanism of transmission is not clearly understood, but contact with a patient is one of the major modes.
Leprosy is common in certain pockets of India, and efforts are being focused on prevention and spreading awareness in these regions. And after decades of testing, the vaccine is finally ready for a roll-out.
Recently, the Indian Council for Medical Research set up an expert committee to strategise on the roll-out of the vaccine, which recommended that it be launched nationwide, targeting major endemic pockets, and cover the entire country by 2 October 2019.
What is the vaccine?
The indigenous vaccine is a heat-killed species of the bacteria called Mycobacterium indicus pranii (MIP) or Mycobacterium w, which can be grown in the laboratory.
The vaccine was developed by a team led by Dr G.P. Talwar at the All India Institute of Medical Sciences in New Delhi in the 1970s.
36 years of testing
In 1983, a small-scale clinical trial was performed to test the efficacy of MIP in the form of a vaccine. In this trial, 32 clinically and histologically leprosy-positive patients with no detectable immunity (lepromin negative) to the bacterium were selected. They were immunised with heat-killed MIP intradermally, and retested for lepromin after 4-6 weeks. The results showed that 20 patients had shown a positive lepromin test (invasion of immune cells in the leprosy-infected areas).
A hospital-based study was performed in the early 1990s on 68 household contacts of patients with no active disease. Fifty-six of these patients showed a lepromin negative-to-positive conversion. After a follow-up dosage of the vaccine, 67 out of 68 showed the conversion. Follow-up with the contacts for 30 months did not demonstrate reversion; there were also no noticeable side-effects. This showed for the first time that the contacts of the patients who are at highest risk of disease can also be immunised against infection.
Further trials were conducted to study the efficacy of the vaccine in combination with standard therapy. In the 2000s, 156 leprosy patients received the vaccine in addition to multi-drug therapy (MDT), the standard treatment for leprosy consisting of a cocktail of drugs. They were compared with a group of 145 leprosy patients who received a placebo injection and MDT. The bacterial load began falling rapidly and significantly in vaccinated patients after 6 months, up to 2-3 years of therapy.
The number of patients testing negative for leprosy after 24-29 months of treatment was 84 out of 133 (63.1 per cent) in the vaccinated group, and 30/120 (25 per cent) in the placebo group.
Further follow-up with the patients was pursued, and “90.2 per cent of patients (146 out of 162) converted from lepromin negativity to positivity in the vaccine group, as against 37.9 per cent (56 out of 148) in the placebo group”. This indicates that 90.2 per cent of vaccinated patients gained cell-mediated immunity against M.leprae.
There were no signs of overt side effects that were usually seen in the patients treated with MDT alone, and a five-year follow-up did not show relapse in patients.
This was one of the indicators that the vaccine developed was safe to administer, and helped in bolstering the patients’ immune system in the long term.
Comparing MIP vaccine with BCG
The MIP vaccine was also compared with the Bacillus Calmette-Guérin (BCG) vaccine, which is part of the national immunisation programme to prevent tuberculosis, but has been found to have some effectiveness against leprosy as well.
In this trial, one group of patients received 12 months of MDT plus BCG intradermally, while the other group received 12 months MDT plus MIP. A third group received 12 months MDT plus normal saline as placebo.
There was a significant reduction in the clinical scores of the patients treated with combination therapy as compared to placebo groups.
Largest trial in Kanpur
The largest clinical trial so far, conducted in Kanpur Dehat, Uttar Pradesh, spanned 272 villages with a population of 420,832. A total of 1,226 multibacillary (MB) and 3,757 paucibacillary (PB) cases of leprosy were detected. Around 24,060 people who had been in close contact with leprosy patients were vaccinated with MIP and with placebo. The dosage efficacy was 68 per cent in the first year, 59 per cent in the second year and 39.3 per cent in the third year.
The effect of the vaccine was sustained for 7-8 years and booster dose was administered to maintain immunity. This study showed that the vaccine is well-tolerated in large populations without the risk of serious side effects.
Following this, the MIP vaccine was approved by the Drug Controller General of India (DCGI) as well as the US Food and Drug Administration (FDA).
Why wasn’t the vaccine put to use immediately?
Leprosy can be completely cured by the use of MDT, which is included as the preferred option in the World Health Organisation guidelines. This approach has shown significant improvement in reducing patient cases, and has been the choice of treatment due to high efficacy and lower costs.
It appears that the implementation of these strategies caused the vaccine to take a backseat for a while.
Finally some movement
The National Leprosy Eradication Programme (NLEP), a Union health ministry initiative which plans and coordinates strategies to tackle leprosy, supported by WHO and several NGOs, launched a pilot programme in 2017, in which the MIP vaccine was used on people who have come in contact with the leprosy patients in four endemic districts of Gujarat — Navsari, Tapi, Bharuch and Narmada.
The trials indicate that the vaccine would be effective in stopping the spread of the disease among the close contacts of the patients, which should effectively reduce the disease burden in endemic areas. However, it remains to be seen if this method will be more effective than the MDT treatment in elimination of leprosy from India.
Atul Khire and Pooja Panwalkar are postdoctoral scientists working in the field of drug discovery and cancer biology. They can be reached at Atul Khire (Twitter ID: @pipetterinchief) and Pooja Panwalkar (Twitter ID: @postdockin).
The views expressed belong to the authors. The article is not medical advice, and in case of any questions/doubts, readers are advised to seek medical opinion from a clinician.