Three healthy people are to receive an experimental Ebola vaccine after U.S. authorities gave the green light for human testing.

More than 3,500 people have been infected by Ebola in Liberia, Guinea, Sierra Leone and Nigeria since the first documented cases in December, according to the WHO. At least 1,900 have died.

The Ebola outbreak in West Africa is much worse than official figures show, and other countries are unintentionally making it harder to control, CDC director Tom Frieden tells CNN.

Crowds flee as healthcare workers forcibly return the man back to quarantine. CNN's MIchael Holmes reports.