Liberia's last known Ebola patient has been released from hospital. But the WHO said Ebola remains "widespread" in Sierra Leone and Guinea.
Healthcare workers, government officials and aid workers saluted the last confirmed Ebola patient as she left the Chinese-built Ebola treatment center in a suburb of the capital, Monrovia.
Beatrice Yordoldo, the patient concerned, said on Thursday: "Today I am very grateful to the almighty God and the Chinese ETU, and all of the Liberian nurses that are working with them. I did not know I could make it."
"This is the last confirmed Ebola case in our country," Deputy Health Minister Tolbert Nyenswah told reporters.
Of 45 samples tested in Liberia last week, none were positive, according to the World Health Organization (WHO), which added that it was first time there had been no new confirmed cases since May 26, 2014.
Some 24,000 people have been infected with the virus since December 2013, nearly all of them in Liberia, Guinea and Sierra Leone. More than 9,800 of them have died, according to the WHO.
But on Wednesday the WHO reported 132 new Ebola cases in West Africa last week; a rise from 99 cases reported the previous week.
The WHO said Ebola remains "widespread" in Sierra Leone. It noted that the number of deaths outside hospital also remains high, "suggesting that the need for early isolation and treatment is not yet understood, accepted or acted upon."
"The Ebola epidemic shows signs of receding but we cannot let down our guard until we reach zero cases," said Marie-Paule Kieny, head of the WHO's Ebola research and development effort.
Sierra Leone has reported the most cases in total at 11,466, including 3,546 deaths. It registered 81 new confirmed infections last week, up from 65 the week before. The new cases were reported in eight different districts across the country, with rising numbers in Freetown, the Western Rural district and in the northern district of Bombali.
The outbreak in Bombali was reportedly linked to a cluster of cases in the Aberdeen fishing community in Freetown. The WHO said efforts were being made to track over 2,000 people associated with the cases.
The number of reported cases has also risen in Guinea where there were 51 new confirmed cases registered in Guinea last week. It marked a significant increase on the 35 new cases reported during the previous seven-days.
Only about half of the new Ebola patients in Guinea are connected to known cases. This means that health officials cannot track where the disease is spreading in the other half of cases.
The WHO said that traditional burials - a high-risk factor for Ebola transmission - continue to take place in both Guinea and Sierra Leone. It added that health workers in both countries are still being attacked by people suspicious of their work.
On Saturday, the WHO is to start testing an experimental Ebola vaccine in Guinea to see how effective it could be in preventing future outbreaks of the virus.
"If a vaccine is found effective, it will be the first preventive tool against Ebola in history," WHO chief Margaret Chan said in a statement.
The two candidate vaccines currently being developed are CAd3 from Britain's GlaxoSmithKline and VSV-EBOV from Merck and NewLink Genetics. Both passed safety tests on humans and are already being tested in Liberia. The trial of VSV-EBOV is due to start in Guinea on March 7.
jm/sms (AFP, Reuters, AP)