An experimental vaccine can slash the risk that children will get malaria, apparently offering the first effective way to inoculate youngsters against one of the world's biggest, most intractable killers, researchers reported yesterday.

An eagerly awaited study involving 2,022 children in Mozambique, in east Africa, found the vaccine cut by one-third the likelihood of getting malaria and reduced by more than half the risk of developing serious, life-threatening cases of the disease.

"We're very excited," said Pedro Alonso of the University of Barcelona, who led the study. "This is the first conclusive evidence that a vaccine that can protect African children against malaria is possible."

While additional hurdles remain, if follow-up studies confirm the findings the vaccine could be available for widespread use within five years, marking the achievement of one of the most elusive goals in modern medicine. The effort to create a vaccine against the mosquito-borne parasitic killer has been marked by repeated failure.

"While much more work on this vaccine is still required, this constitutes a breakthrough in malaria vaccine research," said Marie-Paule Kieny of the World Health Organization.

The malaria parasite infects about 300 million people each year and kills between 1 million and 3 million, mostly children -- making it the most common infectious disease and among the top three killers. Although malaria has been largely eliminated from the United States and Europe, it remains a major public health scourge in the developing world. In Africa, malaria is the No. 1 killer of children younger than 5, claiming the life of one child every 30 seconds by some estimates.