The trial of a Johnson & Johnson vaccine brings the number of Ebola vaccines in such trials to three.
As deaths top 8,000, UNMEER leadership changes hands, and Guinea launches a new effort.
The country has had 337 new cases this week, twice the number in Guinea and Liberia combined.
Bats in a hollow tree and a silent train of transmission may have fueled the unprecedented epidemic.
Scotland detected its first Ebola case, as the illness toll topped 20,000 and the outbreak passed the 1-year mark.
Mishandling of lab material that may have contained live virus follows other CDC safety lapses earlier in the year.
Sierra Leone's western area is seeing intense Ebola activity, and in Guinea a surge of cases in one area propelled the country into its highest weekly case incidence so far.
The authors say the findings have proved useful in creating a more potent version.
The CDC director said Ebola outbreak conditions have improved since his first visit, but tough challenges remain.
In the first stop of a 3-day tour, the UN director warned against easing up on response efforts.
