A worry peculiar to this outbreak, other experts said, was that the rebels in North Kivu might use a declared emergency to embarrass the government by hindering efforts aimed at ending it.

That could make the situation far more dangerous, at a time when the W.H.O. has already asked the United Nations Security Council to send more peacekeeping troops to the area.

Such fears “were briefly considered but were not a factor in the committee’s decision,” Dr. Steffen said.

The committee’s concerns focused instead on the large number of new cases that have been identified with no discernible link to people already infected and on attacks by armed groups in the region, which are obstructing the work of tracing and treating infection, said Dr. Steffen, who is a travel medicine specialist at the University of Zurich.

The Congo has long experience with Ebola, having tackled 10 outbreaks since the disease was discovered in 1976. This includes one this year in remote Equateur Province. It resulted in 33 deaths but was contained in three months by swift international action, including the first widespread use of a new Ebola vaccine.

Health authorities have also rolled out the vaccine to tackle the outbreak in North Kivu, inoculating more than 18,000 people since August. That has helped to slow transmission of the disease, said Tedros Adhanom Ghebreyesus, the World Health Organization’s director general.

“We are better in terms of weapons this time,” he said.

To contain this outbreak, the W.H.O. is considering switching vaccination strategies. It is now immunizing health workers and “ring-vaccinating” all contacts of every known case, but it might try to vaccinate everyone in affected areas, said Dr. Peter Salama, head of emergency responses for the W.H.O.