In Sierra Leone health officials have confirmed a death from Ebola in the country just hours after West Africa was cleared as Ebola-free, the BBC reports.

The World Health Organization (WHO) said on Thursday that active transmission of the deadly virus had ended in Liberia, having previously declared Sierra Leone and Guinea to be Ebola-free in November and December respectively. It was the first time that all three West African countries had held the status simultaneously, effectively bringing to an end the deadliest Ebola outbreak in history that has claimed the lives of some 11,300 people.

Sidi Yahya Tunis, a spokesman for an Ebola test center in Sierra Leone, told the BBC that tests on a patient who died earlier this week confirmed that the death was due to Ebola. Sierra Leonean authorities are now seeking anyone the person may have come into contact with in order to limit the scope of the flare-up. The patient died in the Tonkolli district in northern Sierra Leone after traveling there from Kambia, near the border with Guinea.

WHO officials warned that future flare-ups of the virus were likely. “The risk of re-introduction of infection is diminishing as the virus gradually clears from the survivor population, but we still anticipate more flare-ups and must be prepared for them,” said Bruce Aylward, the WHO’s special representative for the Ebola response, on Thursday.

Recent medical research has found that traces of the virus can remain in the semen of male survivors for up to nine months, though only one case of sexual transmission of Ebola has been recorded.