Sierra Leone was declared free of Ebola in November, but new cases have emerged in Liberia, which had been declared Ebola-free in September.
About 11,000 people died in Guinea, Liberia and Sierra Leone from the disease.
The World Health Organization made the announcement Monday, marking the fact that two Ebola virus incubation cycles have passed since the last person confirmed to have the disease had a second negative blood test.
The transmission of the Ebola virus has officially ended in Guinea, two years after an outbreak started in the African republic and spread to nine other countries. In addition to the original transmission chain, Guinea has had 10 flare-ups from March to November of this year. In one especially unfortunate case, an infant is believed to have contracted Ebola from the breast milk of an Ebola survivor.
But Amesh Adalja, a senior associate at the University of Pittsburgh Center for Health Security, said the fact that transmission had been re-established after the country had been declared Ebola-free has several implications. These appear to have been due to the re-emergence of a persistent virus from the survivor population. "We are not saying the end of the possibility of sporadic cases", Belhocine said, citing Sierra Leone and Liberia where some cases have been registered after the declaration of the end of Ebola.
"Epidemics like Ebola and other things that we have had in the past, like SARS, also highlight a lot of goodwill across the planet to respond to these sorts of humanitarian disasters in the short term".
"At the peak of the epidemic... the country recorded hundreds of cases per week".
The country now enters a 90-day period of heightened surveillance, the UN World Health Organisation said.
They will also pay tribute to the 115 health workers who died fighting Ebola and eight members of an Ebola awareness team who were killed by hostile locals in Womey, in Guinea's forested southeast.
Strong recent growth has been curtailed in Guinea and while Liberia has resumed growth, Sierra Leone is facing a severe recession, according to the World Bank, which has mobilised $1.
Meanwhile, scientists hoping to avoid a repeat of West Africa's nightmare say a trial vaccine continues to show promise.
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