WHO estimates that indoor air pollution kills more than four million people every year around the world.
Disappointed researchers reported Wednesday that a two-year trial in rural sub-Saharan Africa showed clean-burning indoor cookstoves did not reduce cases of pneumonia in young children, as hoped.
Investigators and health advocates had expected that closed stoves rather than smoke-producing open fires would dramatically curb health problems linked with household air pollution.
The World Health Organization (WHO) estimates that indoor air pollution -- notably soot and other fine particles -- kills more than four million people every year around the world, mostly in Africa.
Young children are thought to be especially vulnerable. In Malawi, pneumonia is the leading cause of death among under five-year-olds.
For the experiment, the families of more than 10,000 very young children in villages across two districts in Malawi were divided into two groups.
One continued using traditional, open-fire wood- or dung-burning stoves for cooking and heating for the duration of the two-year experiment.
Families in the other group were given clean-burning cookstoves that also used biomass -- organic matter derived from animals or plants.
"There had been the assumption that the use of cleaner cookstoves will bring about health benefits and save lives," said lead investigator Kevin Mortimer of the Liverpool School of Tropical Medicine.
But the new stoves had "no effect on the incidence of pneumonia" in the children, the researchers concluded.
Published in The Lancet, the study did show that children living in the clean stove homes had 42 percent fewer burns than their counterparts in the other group.
"The reductions in burn-related injuries is encouraging from a safety perspective," Mortimer said.
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