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Vaccine Trials Against Leprosy

 

Dr. M.D. Gupte

 

Several vaccine trials have been conducted in the past using BCG for prophylactic purposes based on the observation of Lepromin conversion (Fernandez 1939) . These studies essentially had problems with respect to design issues, sample size used to be small, control arms were not properly selected and such other problems. However, there are four major studies initiated in the 1960s from Uganda, Myanmar, New Guinea and India. As is widely known, the results are quite different with the range of 24% to 80%.

 

The vaccine trial from India has now been fully analysed and the results are available.

This was a study taken up along with BCG prophylaxis against tuberculosis in South India. It was a double-blind controlled trial with factorial design. Intake for the study was completed between 1968 and 1971. 210,337 individuals were skin tested with PPD-S and PPD-B and vaccinated with one of the selected vaccines. French and Danish strains of BCG in the dose of 0.1 mg and 0.01 mg were used. (In India the usual dose of BCG is 0.1 mg). Dextran was used as a control preparation. Allocation to various vaccine arms was made by individual randomization. Baseline survey for leprosy was taken up five year after vaccination during 1973 t01976 and was restricted to only the vaccinated population. 191,696 individuals (91.4%) from the originally vaccinated cohort were examined. Subsequently, four resurveys were conducted at an interval of 2-1/2 years covering the entire available population.

 

Observed protective efficacy according to the strain of BCG is given in Table-1. Both the strains produced similar type of protective efficacy around 24 to 25%. Observations are available for approximately 484,000 person years for each of 0.1 mg, 0.01 mg and placebo arms. In the placebo arm there were 4,238 cases, in 0.1 mg dose of BCG, 3,213 cases and in the 0.01 mg. BCG arm 3,497 cases of leprosy. Consistent dose effect was seen. 0.1 mg dose of BCG gave a protective efficacy of 24.4% against 17.4% by 0.01 mg dose of BCG (Table-ID . Females were generally better protected but there was no statistically significant difference in the protective efficacy between males and females. Protective efficacy was observed against various clinical form of leprosy to varying extent. However, smear positive cases of leprosy were not prevented by BCG (Table III) . Best protection was observed in the youngest age group of 0-4 years as observed in the first resurvey (57.8%). In the second resurvey it came down to 41.2%. In the third resurvey it was 32% and in the fourth resurvey it was 17.8%. If one considers the cumulative effect, decline in the protective efficacy was from 57.8% between 5 to 7-1/2 years and reached the level of 40.4% between 12-1/2 to 15 years. As mentioned earlier, we do not have the information for the first five years following vaccination. However, baseline prevalence figures were 39.2 per 1000, 42.9 per 1000 and 46.5 per 1000 for 0.1 mg dose of BCG, 0.01 mg dose of BCG and placebo, respectively. Thus, it was evident that there was some protective effect of BCG that could be observed at the baseline survey level. It was also seen that protective efficacy was not affected by PPD-S or PPD-B skin test positivity.

 

 

 

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