Bill Gates said health would remain a priority for the work of his foundation in Africa and it faced a struggle to bring down the rate of new HIV infections in the world's poorest continent.
Speaking to Reuters in the Ethiopian capital Addis Ababa, Gates said the foundation planned to spend $5 billion in Africa in the next five years. The Horn of Africa country is one of the biggest recipients of funds from the foundation.
"Our big priority is health and there is still a lot to be done. The child mortality rate came down from 1990 to the present - it was cut in half, which is fantastic. But that still leaves far too many children dying," he said, referring to pneumonia, diarrhoea and other illnesses.
Turning to HIV/AIDS, Gates said much had been achieved such as an increase in the number of people under treatment for the disease to 12 million globally. But he noted two-thirds of new HIV/AIDS infections continued to take place in Africa.
"It is a mixed situation," he said. "We have a challenge to bring the numbers down."
The philanthropic organisation formed in 2000 by the world's richest man has an endowment of more than $40 billion. It distributed grants of nearly $4 billion in 2014.
Slumping commodity prices have posed serious challenges to economic and political stability in some African countries, and have slowed the momentum of poverty reduction.
But Gates said infrastructure, education and health investment during the boom years had laid solid foundations.
The commodity slump will slow down the pace of development, "but the direction is largely going the right way," he added.