A trial of a malaria vaccine that targets the most dangerous variety of parasite that causes the disease has shown some positive early results.
The vaccine, developed at Oxford University, was 67% effective in a study of 121 men in Kenya, it found.
Encouraging results have now been recorded for two malaria vaccines, after 20 years of research.
Recent tests of a different vaccine in more advanced trials showed signs of it working in young children.
With about 1,300 children dying in sub-Saharan Africa from malaria every day, scientists want a vaccine to protect those most at risk.
According to the World Health Organization, there were 198 million cases of malaria in 2013 and about 584,000 deaths related to the disease.
But it has taken scientists more than two decades to make any real progress, because of the nature of the parasites transmitted to people through the bites of infected mosquitoes.
In total, there are four different parasites that cause malaria. It is not yet known whether the Oxford vaccine protects against all variants of the Plasmodium falciparum parasite or just one.
In the Oxford trial, published in Science Translational Medicine, scientists used two viruses - one a chimpanzee virus - to stimulate the body's immune system to produce cells that can fight against malaria.
This is a novel type of "viral vectored" vaccine that targets the parasite in the liver.
Following up participants after eight weeks, they found the vaccine had reduced the risk of malaria by two-thirds in those who had been given it.
Prof Adrian Hill, director of the Jenner Institute at the University of Oxford, said: "Such high efficacy in this first field trial is encouraging for further testing in children and infants who most need a malaria vaccine."
But malaria transmission levels had been "unexpectedly low" during the trial, the study said, so it was difficult to know how the vaccine would have performed if the malaria risk had been high.
The Oxford researchers are now testing the safety of the vaccine in children and babies in Burkina Faso.
Chris Drakeley, professor of infection and immunity and director of the London School of Hygiene and Tropical Medicine malaria centre, was involved in collating data from final clinical trials of another malaria vaccine in young children, published recently.
Prof Drakeley said it was encouraging to see high protection levels in the Oxford vaccine trial, but there was still a long way to go.
"This research was carried out in a group of adults, when the disease burden is actually in children," he said.
"We also found initially high levels of protection in similar early trials in adults."
He added: "There is no one magic bullet approach. We need a multiple approach, and countries need a tool box of options to fight against the disease."
Mosquito bed nets, insecticides and other malaria control measures continue to play and important role in reducing the burden of the disease.