My favorite underappreciated idea is the brainchild of Jean O. Lanjouw, a University of California, Berkeley, economist who died tragically two years ago. It is an idea that would improve access to medicines in poor countries, cost precisely nothing, and, unlike most plans to improve the world, involve no treaties, summits, or complex international coordination.

During the last half-decade or so, the world has made progress on two fronts of the problem of medical access in poor countries. The first addresses the problem that, even though vaccines for diseases such as polio, yellow fever, and hepatitis B have been around for ages, poor countries can’t afford to buy them, and, during the 1990s, vaccine makers stopped manufacturing them. The solution to this lack of consumer power is costly but conceptually simple: Led by the Bill and Melinda Gates Foundation, aid donors have begun to put money into a vaccine-purchase fund.

The second area of progress concerns the lack of incentive for drug companies to invent new cures for diseases that affect the poor. Practically all of the world’s drug development addresses the health concerns of rich people: Of the 1,233 drugs licensed worldwide between 1975 and 1997, only 13 targeted tropical diseases. The solution here is “advance market commitments,” wherein donors promise to buy a drug that tackles a “poor disease,” committing to purchase a set number of doses at a set price. The first such promise was issued in February. Donors declared they would buy drugs to treat pneumococcal disease, a major cause of pneumonia and meningitis that kills 1.6 million people every year.

Lanjouw’s idea tackles a third part of the drug-access puzzle. It is aimed at diseases that affect everyone in rich and poor countries alike. For these conditions—heart disease,...