Sierra Leone does not yet have enough beds in treatment centers to isolate Ebola patients in the west of the country but the opening of many new facilities in the next few weeks makes its prognosis "very good," the World Health Organization's assistant director general said on Monday.

Unlike the other worst-hit countries, Guinea and Liberia, Sierra Leone has failed to slow or stabilize the spread of the epidemic, raising concern that it may be a weak link in the defense against the virus.

But Bruce Aylward said Sierra Leone, too, was on track to contain the outbreak.