The three West African countries at the heart of an Ebola epidemic recorded their first week with no new cases since the outbreak was declared in March 2014, the World Health Organisation (WHO) said on Wednesday.

The UN agency said that more than 11,000 people have died in Guinea, Liberia and Sierra Leone in the world’s worst known occurrence of Ebola, but there were no new cases in the week to October 4.

New cases of Ebola have dwindled sharply this year but the WHO said there was still a risk of the disease breaking out again.

New cases have dwindled but WHO says there is still risk of the disease breaking out again

“Over 500 contacts remain under follow-up in Guinea, and several high-risk contacts associated with active and recently active chains of transmission in Guinea and Sierra Leone have been lost to follow-up,” it said in its situation report.

Sierra Leone released its last known Ebola patients on September 28 and must wait 42 days until it can be declared free of the disease by the World Health Organisation.

Meanwhile although Liberia received that declaration for a second time on September 3 after a flare-up in June it still remains under heightened surveillance for the deadly virus.

Guinea’s most recent cases were recorded very recently, on September 27.