A new study, published in The Lancet, suggests that malaria kills twice as many people around the world than had previously been thought.
Scientists in the United States and Australia say 1.2 million people died of malaria in 2010.
That is nearly double the number estimated by the World Health Organisation for the year 2009.
The study by the Institute of Health Metrics and Evaluation at the University of Washington found that more than 40% of the victims were older children and adults. This challenges the belief that the overwhelming majority of deaths occurred among the under-5s.
"You learn in medical school that people exposed to malaria as children develop immunity and rarely die from malaria as adults," said lead researcher Christopher Murray.
"What we have found in hospital records, death records, surveys and other sources shows that just is not the case."
From 1985, the paper says malaria deaths grew every year, peaking at 1.8 million in 2004.
However, deaths from the mosquito-borne disease have since been falling sharply due to access to better drugs and insecticide-treated nets.
Rob Mather of the "Against Malaria Foundation" said a humanitarian effort to eradicate the disease in sub-Saharan Africa would have immense economic benefits.
