Liberia Declared Ebola-Free for Second Time

The Ebola virus treatment center where four people are currently being treated is seen in Paynesville, Liberia, July 16. James Giahyue/Reuters

Liberia was declared free of the deadly Ebola virus for a second time on Thursday and entered a 90-day period of heightened surveillance aimed at preventing a future re-emergence of the disease, the World Health Organization said.

Over 11,000 people have died in West Africa since the worst Ebola epidemic on record began over 18 months ago. Liberia has been the country hardest hit with over 4,800 deaths, though it has also had the most success in bringing the outbreak under control.

"WHO declares Liberia free of Ebola virus transmission in the human population. Forty-two days have passed since the second negative test on 22 July 2015 of the last laboratory-confirmed case," the U.N. health agency said in a statement.

During the course of the epidemic, the number of cases has dipped only to flare up again. Liberia was declared Ebola-free in May but a fresh cluster of cases appeared in late June and six additional cases were identified.

Scientists say sexual transmission is the most likely explanation for the resurgence in Liberia since the virus can live on in semen beyond the usual 21-day incubation period.

Neighboring Guinea and Sierra Leone are still struggling to end their outbreaks.

In Sierra Leone, the body of a woman who died on Saturday tested positive for the virus, less than a week after the last person confirmed to have had the disease was released from hospital.

Health workers will vaccinate around 200 people who came into direct or indirect contact with a woman, the WHO said on Wednesday.