GENEVA (AP) — The World Health Organization says it is "cautiously optimistic" about efforts to curb the spread of Ebola in an urban area in Congo, although the lethal virus is still reported in at least two remote areas.

There have been 35 confirmed cases, including 25 deaths. The U.N. health agency and partners have vaccinated more than 400 people with an experimental Ebola vaccine, the first time it has been used in an emerging outbreak.

WHO emergencies chief Peter Salama told reporters in Geneva that the response has gone "quite smoothly" and called it encouraging that there has not been an explosive increase in cases in Mbandaka city.

He says officials are also planning to test five unlicensed drugs for Ebola, pending Congo's approval.