The number of reported Ebola cases has gone up for the first time this year in the three West African countries where transmission is still active.
The World Health Organization says 124 new cases were reported in the week ending February 1 - with a high of 80 new cases in Sierra Leone, compared with 65 in the country the previous week. There were 39 new cases in Guinea, nine more than the previous week, and a total of five new cases in Liberia.
In its latest update, released Wednesday, the WHO said there is an urgent need to end the outbreak before the wet season begins and access to remote areas becomes more difficult.
Since the beginning of the Ebola outbreak there have been almost 22,500 reported cases in the three countries, and nearly 9,000 deaths.
The number of new cases had declined for several consecutive weeks, raising hopes the outbreak was ending.
Health experts have cautioned West Africans against becoming complacent about the disease. The WHO says an unsafe burial last month in Guinea’s Lola district has caused 11 confirmed Ebola cases.
Those killed by the virus remain contagious, and must be buried by workers in protective equipment.
A large-scale trial of two potential Ebola vaccines began Monday in Liberia. Organizers of the study, led by the U.S. National Institutes of Health, aim to enlist a total of around 27,000 healthy men and women for the trial.