To test how well the vaccine protected people, the cluster outbreaks were randomly assigned either to receive the vaccine immediately or three weeks after Ebola was confirmed. Among the 2,014 people vaccinated immediately, there were no cases of Ebola from 10 days after vaccination - allowing time for immunity to develop... In the clusters with delayed vaccination, there were 16 cases out of 2,380.
I really, really hope people were assigned to control and vaccine groups randomly, because aside from the fact that 16 people got Ebola, this is great news. Because of this vaccine, it seems, sixteen other people, who likely also would have gotten Ebola, didn't.
16 out of 2380 is still an amazing improvement.