20 July 2016 Last updated at 08:43 BST
Better education, the availability of drugs that fight the spread of the virus and the prevention of HIV transmission to newborn babies have all played a role.
But it is proving stubborn to get rid of.
As South Africa hosts a major HIV-Aids conference, the BBC's Karen Allen has been to one of the country's HIV hot spots in KwaZulu-Natal.
Remarkable progress has been made in reducing the rate of growth in new HIV infections - the virus that causes Aids.