How effective is the new Ebola vaccine?

"Cautiously optimistic". That's the latest assessment from the World Health Organization on efforts to curb the spread of Ebola which has broken out again in the Democratic Republic of Congo. Some 400 people have been treated with a new vaccine for the virus. That vaccine was actually tested in a trial in West Africa, and one of the principle investigators in the trial was Yazdan Yazdanpanah, head of the infectious and tropical diseases department at Bichat Hospital in Paris. He tells us more.