For the third time, the World Health Organization declined on Friday to declare the Ebola outbreak in the Democratic Republic of Congo a public health emergency, though the outbreak spread this week into neighboring Uganda and ranks as the second deadliest in history.
An expert panel advising the W.H.O. advised against it because the risk of the disease spreading beyond the region remained low and declaring an emergency could have backfired. Other countries might have reacted by stopping flights to the region, closing borders or restricting travel, steps that could have damaged Congo’s economy.
Dr. Preben Aavitsland, a Norwegian public health expert who served as the acting chairman of the emergency committee advising the W.H.O., said there was “not much to be gained but potentially a lot to lose.”
At the same time, the committee of 10 infectious disease experts said in a statement that it was “deeply disappointed” that donor nations have not given as much money as the W.H.O. and affected nations need to battle the outbreak.
But some global health experts have argued in recent months that the W.H.O. should declare an emergency to bring the world’s attention to the Ebola crisis. Dr. Jeremy Farrar, director of the Wellcome Trust, a health foundation based in London, said on Friday that such a declaration would have strengthened efforts to control the outbreak.
“It would have raised the levels of international political support and enhanced diplomatic, public health, security and logistic efforts,” he said.
Dr. Tedros Adhanom Gebreyesus, the W.H.O. director-general, accepted the committee’s recommendation, saying that, even if the outbreak did not meet the criteria for an emergency declaration, “for the affected families this is very much an emergency.”
The W.H.O. has requested $98 million for its response and has received only $44 million. In an interview before the announcement, Dr. Tedros said it had recently received commitments from Britain, the United States and Germany.
“We’ve never seen an outbreak like this,” he said. “It happened in a chronic war zone and overlapped with an election that politicized the whole situation. Militia attacks kept interrupting the operations, and when that happens, the virus gets a free ride.”
With more than 2,100 infected and 1,400 dead, the outbreak centered in eastern Congo is surpassed only by the 2013-16 West Africa outbreak in which more than 28,000 were infected and 11,000 died.
Supplies of the Ebola vaccine are running low, Dr. Tedros said, but Merck agreed Thursday to reopen its plant and make more. To stretch supplies until those arrive, doses are being split and a new Johnson & Johnson vaccine will be rolled out soon, he said.
The outbreak began in August and defied early expectations that it would be contained quickly.
In March, Doctors Without Borders evacuated its personnel from the epicenterafter its clinics in Katwa and Butembo were burned down or overrun as their patients scattered. In April, a Cameroonian doctor working for the W.H.O. was targeted and killed.
The State Department ordered all American personnel — including doctors from the Centers for Disease Control and Prevention — to leave shortly after they arrived last August because of a firefight on the road from their work area to their living quarters.
On Tuesday, the first case outside Congo was detected in Uganda — a 5-year-old boy from a town near the border.
According to the Ugandan and Congolese health ministries, W.H.O. officials and Associated Press reports quoting border officers, the boy was a grandson of a pastor in Congo who fell ill in May. The pastor’s daughter, married to a Ugandan man, went home to care for her father, bringing her two sons, ages 5 and 3. The pastor died on May 27, and on June 10, a dozen members of the family started to return to Uganda.
The children looked sick, and when they were stopped at a border post, their temperatures were taken. They were put in isolation and told to wait while transportation to an Ebola treatment center was arranged. Instead, six members of the family slipped away and crossed on an unguarded footpath to the shallow Lubiriha River, which forms the border but is easily forded.
Only after the pastor’s burial, attended by more than 80 people, was it confirmed that he had died of Ebola. Congolese authorities are trying to find everyone who attended.
Ebola spreads in bodily fluids, including blood and diarrhea, and dead bodies can teem with live virus. Congolese health authorities alerted their Ugandan counterparts, but the 5-year-old was already at a hospital in Uganda, about 15 miles from the border. Since then, both boys and the grandmother have died.
Experts do not expect the Ugandan outbreak to spiral out of control.
Uganda has a strong central government and a cash-starved but organized health care system. It has endured and beaten three previous Ebola outbreaks, in 2000, 2007 and 2012.
On Thursday, Ugandan health officials announced that they had agreed with their Congolese counterparts to set up more health posts at “unofficial points of entry” like those used by the affected family.
Also, with outside help, Uganda has been intensively preparing for Ebola to invade from Congo.
“We’d been expecting it,” Dr. Tedros said. “It was when, not if.”
About 4,700 health workers and others who might come into contact with the infected have been immunized.
Unicef has held over 14,000 meetings at schools, churches, mosques, markets, taxi stands, bus stops and even funerals to discuss Ebola prevention and the need to seek care as soon as symptoms appear.
In eastern Congo, by contrast, the outbreak careered out of control because the area is so lethally unpredictable.
The area is so cut off from the capital, Kinshasa, that 20 people were already dead by the time the presence of the virus was confirmed in their blood samples.
Distrust of the national government there is intense and dozens of local militias and self-proclaimed rebel armies range over it. Health workers have been stopped at informal roadblocks where bandits demand money.
In recent months, experts have been alarmed by an acceleration in infections, though more than 130,000 people have been vaccinated. While it took about eight months to reach the first 1,000 cases, it has taken only a few more to surpass 2,000.
Officials believe many deaths are taking place in villages where families refuse to bring sick relatives in for testing.
Only a little over half of new cases in Congo are in people with known connections to previous cases, an indication that contact tracing, considered essential to beating an outbreak, has fallen apart.
The fatality rate among known cases is about 66 percent, but the number of unknown cases makes the real number impossible to calculate.