Health experts acknowledge they are still unable to track exactly where the virus is still spreading in West Africa, more than 16 months after the first deaths in the remote forests of Guinea. The outbreak has killed more than 11,000 people.
In Guinea, five of the country's nine new cases were detected only after the patients died; none had sought treatment at an Ebola clinic. And only two of the nine cases in Sierra Leone were identified as contacts of previous Ebola patients.
"It will still take some time before we are going to be able to actually celebrate an Ebola-free West Africa," said Peter Jan Graaff, the U.N. secretary-general's acting special representative and head of the United Nations Mission for Ebola Emergency Response.
Graaff emphasized the importance of knowing where the virus is moving within communities. In Guinea, where Ebola first emerged, health workers are still struggling to trace cases.
"As long as we have this, it's going to be very difficult to get to zero. Not impossible — but very difficult," Graaff said.
Health workers have come under attack by fearful Guineans at times during the crisis, who accused outsiders of spreading the disease.
Liberia, which has seen the highest death toll with more than 4,700 lives lost, is poised to declare the outbreak there over on Saturday unless new cases are announced in the coming days.
Associated Press Medical Writer Maria Cheng in London contributed to this report.