It has been 20 years since Bill and Melinda Gates first started using their fortune to address global health issues. By focusing on the diseases that hit the poorest parts of the world the hardest, their foundation has since saved countless lives and prevented untold suffering. “My enthusiasm and belief that this is the right way for this money to be spent is as strong as it was then,” Bill Gates said in a telephone interview with Scientific American before attending a major international health meeting this week in Geneva. But he acknowledged that making progress has not been as simple a process as he at first assumed.

“Some of the naiveté that I had then was that if we created new tools [to identify and treat these diseases] that actually getting them out to people would be fairly straightforward,” Gates says. “And although I was also naive about some of the [drug] discovery stuff and the regulatory complexities, I was even more naive about how tough it is to do delivery.” Fortunately, the Bill & Melinda Gates Foundation and its teams of experts have developed a knack over the past two decades for working out many of the nitty-gritty details of how to get effective treatments to some of the world’s most remote locations—sometimes even redesigning products to make them easier to transport over long distances and across wide-ranging temperatures.

Nowhere has this sort of attention to detail paid off more handsomely than with the effort to reduce—and potentially eliminate—some of the lesser-known ailments that plague the developing world. Collectively known as neglected tropical diseases, or NTDs, these illnesses include leprosy, rabies, blinding trachoma and lymphatic filariasis (also known as elephantiasis). Five years ago a wide range of international organizations (including the Gates Foundation), governments and pharmaceutical companies came together in London to adopt a plan to eradicate many of these diseases by 2020. The drug manufacturers agreed to donate billions of prescription medicines and other treatments if their partners could ensure that they would be used effectively.

The partners are holding a summit in Geneva this week to celebrate the successes they have achieved so far. Health experts have made “record-breaking progress” in getting some of these ancient scourges under control, Margaret Chan, director of the World Health Organization, said in a statement. For example, the organization says only 25 cases of Guinea worm disease were reported in 2016. The number of cases of sleeping sickness (African trypanosomiasis) fell from 37,000 new cases in 1999 to under 3,000 in 2015.

Looking ahead, some of the most exciting news is likely to come in the treatment of lymphatic filariasis, which infects tens of millions of people, causing severe pain and severe swelling in the limbs and other parts of the body. As part of an effort to develop new medications for the disease, researchers funded by the Gates Foundation decided they needed to better understand how current therapies work. In the course of their investigations they learned that if they combined three different current medications, they might be able to neutralize the worms that cause the disease in a matter of months—as opposed to the more typical 15 years.

No one knows why the three-drug combination is better than the standard two-drug treatment. But the three-drug approach has since been fast-tracked for approval, assuming a large-scale efficacy test of 10,000 people confirms positive results at the end of May. Health experts are cautiously optimistic. “We know that we haven’t had any serious adverse events from the combination," says Julie Jacobson, a senior program officer at the Gates Foundation. “If this works, the gain will be huge.”