“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.