No new cases of Ebola were reported in Guinea last week, the first week since the full epidemic began that none of the Ebola-affected countries in West Africa have reported a case, the World Health Organization said Wednesday.

That doesn’t mean Guinea is free and clear — there could be cases that haven’t been detected yet.

But it may be the beginning of a countdown to the end of the epidemic in West Africa that has sickened more than 28,000 people and killed more than 11,000 of them.

Liberia women celebrate in Monrovia, Liberia, 09 May 2015, the news of the end of deadly ebola outbreak in the country. AHMED JALLANZO / EPA

Guinea’s the last of the three heavily hit West African countries to report any recent Ebola. Sierra Leone was declared Ebola-free on Saturday.

“Both Liberia and Sierra Leone have now interrupted all remaining chains of Ebola virus transmission and Guinea reported no confirmed cases in the week to 8 November,” the WHO said in its weekly report on the epidemic.

Four cases were reported in Guinea in the last four weeks, and health workers are watching everyone who’d been close to those patients.

“All 69 contacts currently being followed in Guinea are scheduled to complete their 21-day follow-up period on 14 November,” the WHO said.

“However, 60 of the contacts are considered to be high risk, and one contact from Forecariah has been lost to follow up with the past 42 days. Therefore, there remains a near-term risk of further cases among both registered and untraced contacts.”

WHO says it has people in all three countries keeping a sharp eye out for any suspected Ebola cases. Hundreds of alerts have been reported, but none turned out to be Ebola.

In Guinea, a vaccination campaign is ongoing using a strategy called ring vaccination. When a case is reported, everyone around that person is vaccinated.

“All rings comprised of contacts and contacts of contacts associated with confirmed cases now receive immediate vaccination,” WHO said. Several vaccines against Ebola are being tested in the field.

Ebola has fooled officials before. Liberia was declared Ebola-free in May, but then another case popped up in June.

no one is quite sure where Ebola came from int he first place in West Africa. It hadn't been seen in that region before. So no one's confident it won't come back.

And it's become clear that is some rare cases, survivors might be able to pass the virus along. In Liberia, the very last reported death was a woman engaged to an Ebola survivor, and her only possible known route of infection was through him.