"Case incidence is stable in Guinea, stable or declining in Liberia, but may still be increasing in Sierra Leone," the WHO said Wednesday, stressing that the three countries remain the worst-affected by the virus, with some 600 new cases having been reported in Sierra Leone in the past week.
Only a few cases have been reported in other parts of Africa, Europe and North America.
The current Ebola outbreak started in Guinea in December 2013, later spreading to Liberia, Sierra Leone, Nigeria and Senegal. However, the WHO declared Nigeria and Senegal Ebola-free in October.
The virus is transmitted through direct contact with the bodily fluids of an infected individual. Although there is no officially approved cure for the disease, several countries, including Russia, are currently developing Ebola vaccines.