Afolabi Sotunde/Reuters
The wins include sizable declines in childhood mortality and HIV infection rates, while the ongoing struggles include family planning and equality for women.
In a recent conference call with reporters, Bill Gates named infectious and chronic disease as the two biggest public health concerns in the coming decade.
"The chronic diseases, including things like diabetes or Alzheimer's, neurological conditions, they are increasingly what the big problem is," Gates said. "In a lot of the still-developing countries, you have infectious disease, whether it's malaria, diarrhea, pneumonia, [tuberculosis], HIV, still in very large numbers."
Many of the chronic diseases found in developed or still-developing countries stem from environmental factors, some of which are poorly understood.
In developed countries, for instance, rates of Alzheimer's and dementia have been on the rise for years. In the US, the Centers for Disease Control estimate total numbers will triple by 2050. Scientists have yet to pin down specific causes for the rise, however, and often attribute the increase to factors like genetics, diet, and social engagement.
Other chronic diseases are more straightforward. The greatest killers in the US, for instance, are heart disease and cancer, which collectively are responsible for some 1.2 million deaths each year. Gates said the biggest burdens in these developed countries are research and development costs for creating more effective drugs.
Already, researchers are making inroads toward smarter, more accurate cancer diagnostics. Some American labs have even created experimental blood tests that can diagnose cancer months earlier than the current gold-standard techniques.
"I think you can be pretty hopeful there'll be big progress there," Gates said.
Infectious diseases are a different breed. Disease-carrying insects - like mosquitoes that infect people with malaria - sit beside unclean drinking water, unsanitary living conditions, and poor sexual health practices as major drivers of illness. In these cases, Gates said the burden lay on governing bodies and foundations such as his own to deliver aid to developing nation, while research efforts work on permanent solutions, such as vaccines.
"There isn't the same type of market, the same type of opportunity to charge for drugs there," he said.
As a result, developing countries in East Africa and Central America rely more on outside funding and aid.
One of the biggest concerns for Gates moving forward is HIV. Considerable progress has been made in the last 15 years to slow HIV's growth globally, but funding is slowing down. In the report, Gates expressed concern that a swelling African population could cause the number of new cases to skyrocket in the coming years.
"That's a scary prospect," he wrote. "Without R&D investments, we won't have the new discoveries that will make it easier to prevent the transmission of HIV."