Washington, United States:
New monkey studies show that one shot of an experimental Ebola vaccine can trigger fast protection.
But the effect waned unless the monkeys got a booster shot made a different way.
Some healthy people are rolling up their sleeves at the National Institutes of Health for the first human safety study of this vaccine in hopes it eventually might be used in the current Ebola outbreak in West Africa.
The NIH is publishing some of the research behind those injections.
One reason the vaccine was deemed promising was that a single dose protected all four vaccinated monkeys when they were exposed to high levels of Ebola virus just five weeks later.
That's what researchers report in the journal Nature Medicine.
The bigger challenge is that the protection wanes over time.