The results of the study were reported on Tuesday at an international malaria conference that has drawn some 1500 scientists, health workers and politicians to Cameroon.

The study showed a malaria vaccine offered partial protection to young children for up to 18 months while cutting the risk of severe malaria by 49%.

"It's a very encouraging study because the duration of the efficacy of this vaccine candidate has been shown to be quite long," said Andreas Heddini, a malaria research doctor with no ties to the study.

Cautious optimism

"However, we must bear in mind that efficacy in a study like this and protection are two different things. The study hasn't taken into account how to get the vaccine out to people, because it's done in a controlled environment," said Heddini, who is helping to organise the Cameroon conference.

"But it's encouraging because the duration of the vaccine's efficacy is quite long and opens up possibilities of a vaccine that can prevent people from dying," said Heddini - who added the final creation and approval of any vaccine could take a decade.

Researchers have been working on a malaria vaccine for more than 20 years, but until now none of the candidates showed promise.

"It's a very encouraging study because the duration of the efficacy of this vaccine candidate has been shown to be quite long"

Andreas Heddini,
Malaria research doctor

In the study in Mozambique, 1442 children were administered a three-dose regimen of the vaccine in 2003 and were followed to assess the safety and efficiency of the vaccine.

Specialists agree that, at least for the foreseeable future, there is no prospect of a vaccine that would wipe out malaria like the smallpox vaccine did for smallpox, or even provide lifelong immunity.

But a vaccine that would turn the disease into a mostly mild infection would make a huge dent in the effort to control malaria, which kills a child every 30 seconds and poses a threat to half of all people on the planet.

About 500 million episodes of malaria occur every year, mostly in the developing world. It is the leading killer of children under 5 in sub-Saharan Africa.

Malaria is caused by a parasite carried by mosquitoes.