Epidemiology module of practical skills for mbbs student

Study 6 - Efficacy of BCG in Malawi

Setting: A district in Northern Malawi where BCG was introduced in 1974 using the Glaxo, freeze-dried vaccine

Objectives: To determine the protective efficacy of this vaccine against tuberculosis and leprosy

Design: The presence of a BCG scar was prospectively determined in 83,455 individuals residing in the district and followed from 1979 to 1989 to determine whether they developed tuberculosis or leprosy.

Results: 414 new cases of leprosy and 180 new cases of tuberculosis were identified. Protection against leprosy was estimated at 50% or greater in those with BCG scars, whereas no statistically significant protection could be demonstrated against tuberculosis.

Conclusions: BCG affords better protection against leprosy than against tuberculosis

Lancet 1992;339:636-639