Millions of people in the third world die from diseases that are rare in the first world--diseases like malaria, tuberculosis, and schistosomiasis. AIDS, which is now usually treated in rich countries, still ravages the world's poor. Vaccines offer the best hope for controlling these diseases and could dramatically improve health in poor countries. But developers have little incentive to undertake the costly and risky research needed to develop vaccines. This is partly because the potential consumers are poor, but also because governments drive down prices.

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