updated 2/2/2012 7:14:10 PM ET 2012-02-03T00:14:10

Malaria may be killing around twice as many people as experts previously thought, and it could also be hitting older children and adults — long considered the least susceptible — a new study suggests.

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Malaria cases and deaths have been dropping since 2004, due largely to big campaigns to distribute bednets, spray homes with insecticide and make better drugs available. In December, the World Health Organization reported about 655,000 had died from the disease in 2010.

But researchers using newly available data and modeling tools put the 2010 figure at about 1.2 million, about 90 percent of which are in Africa.

The findings also challenge the belief that children who grow up in areas with malaria develop immunity to the disease as they get older. Doctors have long thought children under 5 years old and pregnant women were the most susceptible to the mosquito-borne disease.

"That assumption appears to be wrong," said Stephen Lim of the Institute for Health Metrics and Evaluation at the University of Washington, one of the study authors.

"We need to shift our strategies to try protecting everyone, not just children under 5 and pregnant women," he said.

Lim and colleagues analyzed data on malaria deaths from 1980 to 2010, including information not used in prior studies. They made statistical adjustments for deaths that may have been misclassified, including those in adults. They also developed several models to predict how many people likely died of malaria. The study was paid for by the Bill & Melinda Gates Foundation and was published Friday in the journal, Lancet.

Other experts weren't so convinced by the new figures.

"I wouldn't worry unduly about what the (malaria) numbers are," said David Schellenberg, a professor of malaria and international health at the London School of Hygiene and Tropical Medicine.

He said most people killed by the disease aren't hospitalized, making their deaths hard to track, and most malaria estimates are based on patchy and incomplete information. He was not linked to the study.

WHO malaria expert Richard Cibulskis, however, said WHO stood by their estimates.

"We're not sure why they're coming up with this result, but we suspect it may be overdiagnosis." Cibulskis said he wasn't convinced there were significant numbers of malaria deaths in adults and said other studies haven't found this.

He said data from both WHO and the new Lancet study showed the same overall trend, that malaria has been dropping since 2004, due largely to widespread campaigns to fight the disease.

Cibulskis said he was worried the current financial crisis could jeopardize successes in the battle against Malaria. Last year, the Global Fund to Fight AIDS, Tuberculosis and Malaria — which pays for about two-thirds of the world's malaria programs — announced it had run out of money for future grants.

"If we take our foot off the accelerator, malaria could come roaring back," Cibulskis said.

Lim and colleagues projected malaria deaths wouldn't fall below 100,000 until after 2020. That could make reaching certain targets — such as the United Nations' aim of cutting malaria deaths to "near-zero" by 2015 — tricky. "It's unlikely that goal will be met," Lim said, adding a few more decades might be necessary. "Based on what we are seeing, there may be a need to rethink the timeline for malaria elimination."

Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.


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