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 in the region. Dr. Jeremy Farrar, director of the Wellcome Trust, a major 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 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 epicenter after 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 in the Kasese district, 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, including the pastor’s 50-year-old widow, started to return to Uganda.
The children looked sick, and when they were stopped at the Kasindi border post, their temperatures were taken. They were put in an isolation area and told to wait while transportation to the Ebola treatment center in Beni was arranged. Instead, six members of the family slipped away and crossed via an unguarded footpath to the shallow Lubiriha River, which forms the border but is easily forded.
Only after the pastor’s burial, which was 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. In the past, funerals at which many mourners washed or touched the body have become “super-spreader” events.
Congolese health authorities, who had taken the family’s names and cellphone numbers, alerted their Ugandan counterparts, but the 5-year-old was already at Kagando Mission Hospital, about 15 miles from the border. Since then, both boys and the grandmother have died.
The rest of the family, including the father, a baby and a maid, were moved — with their consent, the Ugandan health ministry said — into Congo, to the Beni treatment unit, which has experimental therapies against the disease.
As a result, there are now no confirmed cases of Ebola in Uganda, the ministry said Thursday.
For the moment, experts do not expect the Ugandan outbreak to spiral out of control.
Uganda has a strong central government, a cash-starved but organized health care system and less ethnic and political conflict than most other east African countries. 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.
“This was not a surprise,” Dr. Tedros said. “We’d been expecting it. 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. It has also supplied water, toilets and hygiene supplies to more than 500 clinics and hospitals and trained their staff members in infection control.
In eastern Congo, by contrast, the outbreak careered out of control because the area is so lethally unpredictable.
Disaster on the current scale was not anticipated because an earlier outbreak in Congo’s western Équateur Province — a relatively peaceful farming and river-market area — that began in April last year ended in just three months with only 33 deaths. That was considered a triumph for the rapid response of a newly re-energized W.H.O. and particularly for the new Merck rVSV-ZEBOV vaccine.
The vaccine, used to inoculate all the contacts of each known case, was hailed as a game-changer: Only 3,300 doses were needed to quell the Équateur outbreak, even though it reached Mbandaka, a river city of 1.2 million people.
The outbreak in North Kivu, 1,500 miles to the east, was detected only a week after the Équateur one was declared over. But the area where it exploded 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.
Eastern Congo is a vast, often violent place. Distrust of the national government is intense and dozens of local militias and self-proclaimed rebel armies range over it, sometimes engaging in fierce firefights with the army, police and United Nations peacekeepers.
Health workers have been stopped at informal roadblocks where bandits demand money; some have been attacked and killed.
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 and fear the vaccine.
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.
Last month, health officials modified their vaccination tactics: Along with “ring-vaccinating” contacts of known cases, they began “pop-up” operations in areas considered safe but close to known case clusters, offering smaller doses to anyone willing to take them.
There are now 14 treatment or isolation units in Congolese towns considered relatively safe, and some have four experimental treatments on hand. Early results were encouraging, but many patients arrive already riddled with virus and in the throes of organ failure, beyond hope.
The fatality rate among known cases is about 66 percent, but the number of unknown cases makes the real number impossible to calculate.
Ebola is not Congo’s only health problem, Dr. Tedros noted, and possibly not even its biggest. It has recently seen almost 100,000 cases of measles with 1,500 deaths. And cholera is spreading. The W.H.O. is helping distribute 3.4 million doses of vaccine against measles and 800,000 against cholera.
“We go to the communities and people say: ‘Why are you focusing on Ebola? We’re dying from measles, from cholera, from malaria, we have no clean water,’” he said. “The world should be supporting Congo in a very comprehensive way.”