The BCG vaccine for tuberculosis (TB) isn't working. The disease is rampant in tropical countries where vaccination programmes have been intensive, making the World Health Organization's ambition of a TB-free world by the year 2000 a forlorn one.
The vaccine is just 22 per cent effective in Kenya, and 20 per cent effective in some areas of India. Its protection over time also seems to wear off. In one trial in south India, its efficacy fell from 80 per cent to zero in 20 years, reports Prof P Fine at the London School of Hygiene and Tropical Medicine, in a special analysis for The Lancet.
Overall effectiveness ranges from zero to 80 per cent around the world, with the variation due possibly to strain variations, genetic or nutritional differences, and to environmental influences. One theory maintains that high latitude makes the vaccine more efficient, possibly accounting for 41 per cent of variations.
These variations were known by scientists as far back as the 1950s, when it was discovered that the vaccine offered 75 per cent protection in the UK, against just 30 per cent in Georgia, Alabama and Puerto Rico.
Nonetheless, it is the most widely used vaccine in the world, and is likely to remain so as, paradoxically, it has been discovered to offer wonderful protection against leprosy, even when it is useless against TB. In Kenya, where TB protection is just 22 per cent, the vaccine offers 81 per cent protection against leprosy, and 54 per cent in Malawi, where its efficacy an an anti-TB agent is zero (The Lancet, November 18, 1995).