One such challenge is chronic hepatitis C infection, which afflicts an estimated 170 million people worldwide. Since its discovery 25 years ago, hepatitis C has become the leading indication for liver transplant in the United States and a common cause of liver failure around the world. For some, however, it is about to become eminently curable.

When I trained as an infectious disease physician in the mid-1990s, I traveled frequently between Boston’s teaching hospitals and rural Haiti. AIDS had become a leading cause of death in both places but was rapidly declining in Boston while soaring in Haiti, as it was across Africa.

This divergence was thrown into relief at a 1996 AIDS conference where researchers presented data showing that combination antiretroviral therapy could transform HIV infection from a death sentence into a manageable chronic disease. The conference’s theme that year was “One World, One Hope.” A coalition of activists, noting the $15,000 annual cost of the lifesaving drugs and the lack of an international plan for ensuring access among those living in poverty, held up their own signs reading “One World, No Hope.”

By 2000, more than 6 million people were dying in poor countries each year from HIV, tuberculosis and malaria — diseases for which effective therapeutics were available to those who could afford them. Here was a failure not of science but of delivery.

Thankfully, and in no small part because of the relentless efforts of AIDS activists, an abiding cynicism about the limits of an international response to these pandemics gave way to an unprecedented “delivery decade.” This was inaugurated in the early 2000s with the U.S. President’s Emergency Plan for AIDS Relief and the Global Fund to Fight AIDS, Tuberculosis and Malaria.

As I recounted in the New England Journal of Medicine in December, linking this funding to effective delivery mechanisms had profound effects in some of the world’s poorest and most disrupted places. By the end of 2012, almost 10 million patients in low- and middle-income countries were on antiretroviral therapy. In Haiti and Rwanda, AIDS-related mortality rates fell more sharply than in the United States after its introduction of antiretroviral therapy in the mid-1990s.

Visit The Washington Post to read the full op-ed by Dr. Paul Farmer.