Not a single person tested positive for Ebola last week in the three West African nations devastated by the deadly virus, the first time that has happened since March 2014, the World Health Organization reported Wednesday.

The epidemic that killed more than 11,000 people and sparked panic in the Unites States during the summer of 2014 is now confined to small areas of Guinea and Sierra Leone, the international health agency reported.

There have been fewer than 10 cases per week over the 11 weeks that ended Sept. 27. From Sept. 28 to Oct. 4, no cases were confirmed in Liberia, Guinea or Sierra Leone. At the height of the epidemic, in mid-September 2014, the three countries recorded more than 700 confirmed, probable or suspected cases of the deadly hemorrhagic virus in a single week.

In all, 28,457 people have been infected by the virus and 11,312 have died. Since the outbreak began early last year, 881 health workers were infected and 513 died. Thomas Eric Duncan, a Liberian who arrived in Texas with the virus, and Martin Salia, a doctor who was working at a hospital in Sierra Leone, were the only people to die of Ebola on American soil.

In general, the epidemic is considered over in a country when no new cases are identified for 42 days, twice the incubation period of the virus. The WHO declared the epidemic ended in Liberia on May 9, but a new case was reported at the end of June. It sparked a small cluster of additional infections that was controlled. On Sept. 2, Liberia had again gone 42 days without a new case.

That is not yet the case in Sierra Leone and Guinea, the WHO reported. In Guinea, 509 people who were in contact with people believed to have the virus are still being monitored, and another 290 have been identified but have not been found. Several other people from both countries "have been lost to follow-up," the WHO reported.

In Sierra Leone, all contacts of the most recent chains of transmission have completed 21-day follow-up without contracting the virus. But two people considered "high-risk" contacts have not been found.

Read more:

For more health news, you can sign up for our weekly newsletter here.