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A vaccine for leprosy

Print edition : Mar 21, 1998 T+T-

The development of a vaccine to counter multibacillary leprosy is a significant event for India, which has the largest number of leprosy patients in the world.

A VACCINE to "immunise" patients suffering from a severe type of leprosy, called the Multibacillary (M.B.) leprosy, has been developed by Dr. G.P. Talwar, founder-Director of the National Institute of Immunology. The vaccine, Mycobacterium w (the code name under which this species of bacteria was investigated), was launched in the market on January 30. The institute has also received from the Drugs Controller of India authorisation for its commercial production. "While research on a leprosy vaccine goes on in many parts of the world, this is one which has signalled the end of the search," Talwar told Frontline.

The M.B. type is a severe type of leprosy. Patients afflicted with it serve as reservoirs of infection. They have failed to respond to lepromin, the antigen for ordinary cases of leprosy.

Nearly 99 per cent of all human beings are resistant to leprosy and are able to eliminate M.leprae infection, according to epidemiological studies. Among those who are afflicted with the disease, nearly a quarter contract the M.B. type. They are the ones who serve as a hospitable base from which the bacilli can spread, wrote Talwar in his paper titled 'An Immunotherapeutic Vaccine for Multibacillary Leprosy'. Only the administration of drugs for two to five years was found to cure patients of the M.B. grouping. "Multibacillary patients need a long period of treatment," Talwar says.

In the clinical trials conducted so far, the Mw vaccine has been found to be effective when used in combination with chemotherapy and immunotherapy. The vaccine has gone through three phases of clinical trials in rural and urban leprosy control centres. While Phase I involved the administration of the vaccine to M.B. leprosy patients who had gone through chemotherapy, Phases II and III explored its preventive or immunoprophylactic potential. However, owing to the long latent period of the disease (two to 10 years), Talwar said that immunoprophylactic studies would need up to 12 or 15 years to get conclusive results. However, he said that trials were being conducted in a community block of Kanpur Dehat in tandem with the National Leprosy Eradication Programme and in collaboration with the Uttar Pradesh Health Directorate. A similar trial was on at Chengalpattu in Tamil Nadu, he said.

The vaccine's potential to confer immunity on M.B. leprosy patients was also explored. The vaccine was administered along with the standard multi-drug treatment (MDT) recommended by the World Health Organisation (WHO) to two groups, one in Delhi and the other in Kanpur Dehat. It was found that this shortened the treatment period. Besides, considerable clinical improvement was noticed with two or four doses of the vaccine. Talwar said that an independent study by the Leprosy Research Institute in Agra showed that the lepra bacilli in M.B. patients with a Bacillary Index were rendered non-viable within six months of combined treatment with multiple drugs and one or two injections of the Mw vaccine. It was found that M.leprae continued to thrive in patients who were not given the vaccine but were administered only chemotherapy with the recommended MDT.

The advantages of the vaccine are that it expedites "bacterial clearance" and "accelerates clinical regression of lesions", according to Talwar. During clinical trials, a faster rate of decline of the bacteriological load was detected in patients who were given the vaccine, compared to those who received only the MDT and a placebo. The vaccine was found to upgrade immunity and help clear granulomas (lesions) quickly. No reactions were caused other than those noticed during MDT therapy. By killing the M.leprae within six months, the vaccine ensured that the disease did not spread from the patient.

Talwar said that while the prevalence of leprosy had gone down in some countries, the incidence of the disease continued to be alarming in many others, including India. He said that this was because of the continuing existence of a foyer of infection.

The development of the vaccine is a significant achievement. Since the 1970s, when there were around four million leprosy patients in India, it was felt that the eradication of the disease was impossible unless its spread from the principal reservoir, that is, human beings, was controlled. The disease is prevalent in several states of India, which has the largest number of leprosy patients in the world. What is alarming is the latent gestation of the disease. The M.B. type was found to be non-auto-regressive unlike other forms such as tuberculoid leprosy, Talwar said.

In a paper published in 1978, Talwar, who was then the head of the Indian Council of Medical Research(ICMR)-WHO Training Centre in Immunology at the All India Institute of Medical Sciences, New Delhi, pointed out that the latent period of the disease was long and many patients could be agents of transmission even before they were spotted and treated. The research on the vaccine began then. Although the research began at the AIIMS, it was during his tenure as the Director of the NII that clinical trials with the Mw vaccine were conducted.

"This vaccine will play a very important role in the eventual eradication of leprosy," said Talwar, a recipient of the Padma Bhushan. He is currently Professor of Eminence and Senior Consultant at the International Centre for Genetic Engineering and Biotechnology.