Despite this progress, the mosquito-borne disease remains a serious problem in the developing world, said Dr. Robert Newman, who heads WHO's global malaria program. There were more than 200 million cases of malaria in 2012, and the disease killed an estimated 627,000 people last year.

"The burden is not equally distributed," Newman told reporters at a briefing in Washington Wednesday. Seventeen countries in the world account for 80 percent of the malaria deaths, he said. Sixteen of those countries are in Africa. The other country in that group is India.

Nevertheless, Newman calls the 45 percent reduction in malaria deaths a huge turnaround. "That's pretty astonishing for a disease that had been neglected and abandoned," he said. "People had decided that [malaria] is just something you have to live with in Africa, in Asia, in the Americas."