Saving a life usually grabs more attention than preventing a death. Perhaps that is why the achievements of drugs—antibiotics, anticholesterol treatments, and countless others—have overshadowed those of simple vaccines. Yet the vaccines for polio and smallpox have been two of the greatest public-health triumphs of the past 100 years. From a developing country's point of view, immunization still promises the most cost-effective public-health strategy for maladies ranging from measles to polio to tetanus. It will be a long time before the world's most devastating infectious diseases are eradicated, as smallpox has been, thus making vaccination against them unnecessary. In the meantime, preventing their occurrence through vaccination is vastly cheaper than caring for their victims, but the economics of drug development often don't line up with the economics of health care provision in poor nations.

Sometimes, the result is that no vaccine gets developed. Two million people, mostly in the developing world, die of malaria annually, but only in the past five years has there been a concerted global effort to develop a vaccine against it. In other cases, vaccines do exist but are too expensive for the markets in question. For example, though a vaccine for the pneumococcal disease—a...