One day after the West Africa region that suffered a two-year Ebola epidemic was declared free of the deadly disease, Sierra Leone has confirmed another death from Ebola. The World Health Organization says there's still a risk of more flare-ups.

Officials are now trying to trace any contacts the person who died may have had, in a desperate attempt to cut short a potential new chain of transmission.

"Specialists have been warning that an outbreak could easily flare up again," NPR's Ofeibea Quist-Arcton reports for our Newscast unit, "because even survivors may continue to harbor the Ebola virus in their bodily fluids — including semen and breast milk — and pass the infection onto others."

Sierra Leone was declared Ebola-free in November; since then, health officials have made similar declarations for Guinea and Liberia, the other two nations that saw thousands of people die from the disease.

"We are now at a critical period in the Ebola epidemic as we move from managing cases and patients to managing the residual risk of new infections," Dr. Bruce Aylward of the WHO said Thursday.

Researchers are still learning about Ebola, which has been found to survive in people for nine months or more.

"The reality is this outbreak's not over," Dr. William Fischer of the University of North Carolina told NPR back in November, after new Ebola cases had been reported in Liberia. "It's just changed."

As Camila reported for the Two-Way Thursday, Liberia "had previously been declared Ebola-free in May and in September last year. Each time, at least one new case was later discovered."

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