A nurse vaccinates a child against Ebola in Beni, Congo, on July 13. (Jerome Delay/AP)

The nearly year-long Ebola outbreak in Congo is now a “public health emergency of international concern,” the World Health Organization declared Wednesday. The designation by the WHO — an international body charged with coordinating global response to disease — came 11 months after the outbreak began in Congo’s conflict-ridden North Kivu province.

The deadly virus has since infected more than 2,500 people and killed nearly 1,700, Congo’s Health Ministry says. Health officials worry it could spill over borders to Uganda, Rwanda, Burundi and South Sudan.

But the emergency declaration has proved controversial. Here’s what you need to know:

What is a “public health emergency of international concern”?

It’s a designation that emerged from international health regulations issued in 2005, which defined such an emergency — PHEIC, in global health parlance — as an “extraordinary event” that could spread to other countries and demanded a coordinated global response.

The WHO director-general decides when and where to apply the label after consulting a 10-member committee of experts. That committee also recommends when to end the global health emergency.

The WHO has applied the label four times in the past: in response to the swine flu epidemic in 2009; the spread of polio viruses in several countries in 2014; the 2014 Ebola outbreak in West Africa; and the 2016 Zika epidemic in the Western Hemisphere.

The designation is essentially the public health equivalent of hazard lights, signaling to countries around the world that they should pay attention to the situation and contribute to the response.

But the WHO doesn’t declare emergencies lightly. The label can also spark fear in neighboring countries, which can lead to those countries shutting down travel or trade with the country at the epicenter of the health crisis.

Why did the WHO declare one in Congo now?

The WHO declined to label the Ebola outbreak in Congo a global health emergency three times before it finally did so Wednesday. It’s unclear what tipped the scales, but the WHO emergency committee cited a recent case confirmed in the city of Goma as one catalyst, according to a WHO news release.

Goma is a city of nearly 2 million people in eastern Congo. It lies on the border with Rwanda, the most densely populated country on earth. Tens of thousands of people cross the border on foot each day, and health officials worry that Ebola could cross with them.

Robert Steffen, chairman of the WHO emergency committee, also pointed to heightened transmission of the disease in the northeastern city of Beni and recent attacks on health workers as additional reasons for elevating this Ebola outbreak to emergency status.

“There must be more engagement by the global community to end this outbreak,” Steffen said Wednesday.

What does it mean?

Not much, on its own.

The label does not automatically trigger funding or kick into gear specific response programs. Moreover, some international actors had already pledged support. The United States, for instance, had already labeled the outbreak an emergency, and Britain has donated millions to halting the disease.

But the WHO designation does hold important symbolic value, according to Paul Farmer, a Harvard Medical School professor and founder of nonprofit health organization Partners in Health.

It facilitates coordination between the WHO and countries around the world, and can put pressure on wealthy countries and international organizations to donate money and personnel to fighting the disease.

Tedros Adhanom Ghebreyesus, director-general of the WHO, wrote on Twitter that “a public health emergency of international concern is not for fundraising, it’s for preventing the spread of disease.”

Ghebreyesus wrote that he is not aware of donors withholding funding in the absence of an emergency declaration. But, he added, “if that was the excuse, it can no longer be used.”

The emergency committee said funding delays have hampered the response to this Ebola outbreak, and they called on countries around the world to step up.

J. Stephen Morrison, a senior vice president at the Center for Strategic and International Studies in Washington who has studied the outbreak, estimated that the WHO may aim to raise about $300 million to contain Ebola and treat the sick in Congo over the next six months.

“Without this declaration, there’s been a problem with mobilizing resources over the long range,” he said. “The resources required are escalating really rapidly.”

Experts say the next step will probably be a pledging conference, which will convene the WHO, World Bank, United Nations, United States, Britain and other major donor countries to commit funds to stopping the crisis.

Morrison said the emergency declaration also serves to catch the attention of global decision-makers and bodies such as the U.N. Security Council, which can help develop and implement response strategies.

“Hopefully this will bring greater money, a strategic plan, much greater accountability; hopefully it will focus high levels on cracking the security problem and community resistance,” he said.

As countries step forward to respond, Farmer urged them to prioritize caring for the sick in what he called a “health desert.” Too often in the past, he said, response efforts have elevated containing the outbreak over treating those affected.

“Every time that we say ‘a public health emergency,’ it should mean it’s a clinical emergency,” he said. This means making resources available so that “anybody who gets sick is promptly diagnosed and cared for.”

Congolese officials announced Thursday that soldiers and police would begin enforcing hand-washing and fever checks in the wake of the emergency declaration, the Associated Press reported.

What are the potential downsides of an emergency declaration?

Not everyone is happy about the declaration. Congo’s government raised concerns about affixing the emergency label to the outbreak, fearing it could generate paranoia and damage trade and travel.

The last time the WHO declared a global health emergency for an Ebola outbreak — in West Africa in 2014 — many countries stopped granting visas to people from Liberia, Guinea and Sierra Leone, STAT news reported. Some airlines also stopped flying to those countries, preventing health workers and supplies from reaching the disease’s epicenter.

WHO officials called on neighboring countries Wednesday to keep their borders open after the emergency declaration.

Steffen said it should not be used “as an excuse to impose trade or travel restrictions, which would have a negative impact on the response and on the lives and livelihoods of people in the region."

What happened the last time the WHO labeled an Ebola outbreak an emergency?

When the WHO declared the 2014 Ebola outbreak an emergency in August of that year, eight months after its start, the designation was widely seen as “woefully late,” Morrison said.

At that point, the outbreak had already spread to major population centers in three countries. It took nearly two years after the emergency declaration for health workers to quell the crisis, which killed more than 11,000 people, according to the Centers for Disease Control and Prevention. West Africa was finally declared free of Ebola in June 2016.

The WHO received widespread criticism for its handling of the 2014 Ebola crisis. Since then, it has changed its emergency problems “very effectively,” Morrison said. It has added contingency funds that weren’t available before, among other measures.

But it’s unclear whether an emergency declaration will prove more effective at nipping Ebola in the bud this time around.

New vaccines have greatly improved prevention efforts, though they remain underproduced. Farmer said Uganda and Rwanda are relatively well-prepared to handle Ebola cases. But South Sudan is “completely ill-prepared,” he added.

Armed conflict further complicates the response to this outbreak. Congo is an active war zone, and violence has at times forced health workers to pause their efforts — particularly as local suspicions have fueled violent attacks on health workers.

“It is the worst imaginable environment to try to arrest an Ebola outbreak,” Morrison said.