Dr. Margaret Chan, the director general of the W.H.O., said in a news briefing that she was accepting the recommendation of an emergency committee, which concluded that West African countries had the ability to contain the small number of new cases that continued to arise, and that “the likelihood of international spread is low.”
Dr. Chan called on nations that had imposed restrictions on interaction with the three countries to “immediately lift any ban on travel and trade.”
The Ebola outbreak, ignited in Guinea in December 2013, ultimately sickened more than 28,000 people in Guinea, Liberia and Sierra Leone, killing more than 11,300. But the W.H.O. said in a statement that all three countries had made it successfully through a 42-day observation period and a 90-day surveillance period without any cases linked to the original transmission chain for the virus. The last country to achieve that status was Guinea, which completed the 90-day period two days ago.
“The original Ebola outbreak has come to an end. The original chains of transmission are terminated now,” said Dr. Robert Steffen, a communicable disease expert who is vice chairman of the W.H.O. emergency committee.
Still, flare-ups of cases continue, an expected consequence that has occurred with other Ebola outbreaks, W.H.O. officials said. The most recent is a cluster in Guinea of five confirmed and three probable cases, which the W.H.O. said it was treating as a moderate-level crisis. In all, there have been 12 new clusters of cases in the three countries since the original transmission chains were extinguished, but they have been occurring less frequently, the W.H.O. said.
“We know that little clusters will continue to flare up — that will be normal life,” Dr. Steffen said.
He added that most of the flare-ups had probably been transmitted through the semen of Ebola survivors.
Dr. Bruce Aylward, the W.H.O.’s chief of emergency responses, said that studies following survivors had indicated that in, at most, 2 percent of men, Ebola could persist in semen “for more than a year, out until 15 months.” He said scientists had not determined why these men continued to hold traces of virus in their semen and others did not.
Dr. Aylward said that the current Ebola cluster in Guinea was linked to a single transmission chain from one village, and that more than 900 people who had had contact with the patients were being followed “in an effort to bring this to a rapid close.”
Asked whether downgrading the emergency status of the Ebola outbreak would allow the W.H.O. to redirect resources to the Zika virus crisis, the officials essentially said no.
“We’d love to say it allows us to step down a little and refocus,” said Dr. Aylward, but the agency considers it important to keep hundreds of its employees in the West African countries.
“A high level of vigilance and response capacity must be maintained to ensure the ability of the countries to prevent Ebola infections and to rapidly detect and respond to flare-ups in the future,” Dr. Chan said.