The World Health Organization on Wednesday declared coronavirus a pandemic, reflecting alarm that countries aren’t working quickly and aggressively enough to fight the disease it causes, covid-19.

“We are deeply concerned both by the alarming levels of spread and severity and by the alarming levels of inaction,” said WHO Director General Tedros Adhanom Ghebreyesus.

For weeks now, the WHO has hesitated to make the pandemic declaration, for fear of inciting panic or prompting some countries to flag in their efforts, even though many epidemiologists believed the coronavirus had already spread to pandemic levels.

But on Wednesday, Tedros noted the widespread scale of the outbreak. “There are now more than 118,000 cases in 114 countries, and 4,291 people have lost their lives,” he said. “In the days and weeks ahead, we expect to see the number of coronavirus cases, the number of deaths and the number of affected countries climb even higher."

Tedros cautioned that “‘pandemic’ is not a word to use lightly or carelessly. It is a word that, if misused, can cause unreasonable fear, or unjustified acceptance that the fight is over, leading to unnecessary suffering and death.”

The WHO’s announcement does not trigger any new funding, protocols or regulations. But it is an acknowledgement of the disease spreading across several continents.

What is a pandemic, and who gets to define it?

Disease experts use the term “pandemic” to describe when an epidemic has become rampant in multiple countries and continents simultaneously. (The term comes from the Greek word “pan,” meaning “all,” and “demos,” meaning “people.”)

While the word may evoke fear, it describes how widespread an outbreak may be, not its deadliness.

“I think one of the things people misunderstand when it comes to pandemics is it’s not about how severe it is or how many cases there are or even how worried we need to be. It’s about literal geography,” said Caitlin Rivers, epidemiologist at the Johns Hopkins Center for Health Security.

The WHO — the global body with authority to officially declare a pandemic — defines pandemic loosely as “the worldwide spread of a new disease.” The U.S. Centers for Disease Control and Prevention defines it this way: “Pandemic refers to an epidemic that has spread over several countries or continents, usually affecting a large number of people.”

Why did the WHO finally say the p-word after resisting so long?

WHO officials on Wednesday seemed to indicate the declaration was fueled by frustration with slow and inadequate responses by some countries as the virus has spread.

“We have called every day for countries to take urgent and aggressive action. We have rung the alarm bell loud and clear,” Tedros said. “We cannot say this loudly enough or clearly enough or often enough: All countries can still change the course of this pandemic.“

Michael Ryan, WHO director for health emergencies, said there is “no mathematical formula, no algorithm,” for making a pandemic declaration. He said the decision came after serious internal and external consultation, “because we understand the implication of the word.”

Ryan said the declaration is aimed at “galvanizing the world to fight” and not as a reason for government “to give up or to grow fear.”

“There is a real chance to blunt the curve; there is a real chance to bend the curve and reduce the number of cases that our health system has to cope with,” Ryan said.

WHO officials on Wednesday noted that countries such as South Korea and China have demonstrated that the virus’s outbreak can be suppressed and controlled through old-school public health measures of aggressive contact tracing, quarantines and isolation of the sick, social distancing and mobilization of the public to sanitize and prevent transmission.

“Some countries are struggling with a lack of capacity,” Tedros said. “Some countries are struggling with a lack of resources. Some countries are struggling with a lack of resolve.”

They also expressed worries that if stronger actions are not taken, the outbreak could spread to countries weak health systems, such as those in sub-Saharan Africa, which could lead to an explosion of cases and deaths.

Does it mean countries should change how they’re fighting the virus?

In the past, health experts have used a pandemic declaration as a signal that efforts to contain an outbreak from spreading have failed and that countries should focus their efforts more on mitigating its effects through actions such as getting hospitals ready to handle an influx of patients, stockpiling materials and enacting social distancing policies.

This outbreak has behaved differently, however, and the WHO has stressed in recent weeks that all countries should focus on containment even as they begin ramping up efforts to mitigate. By working to contain the virus, countries can slow down the spread of the disease and buy time to work more on mitigation strategies.

“It would be a mistake to abandon the containment strategy,” Tedros said. “We have never before seen a pandemic sparked by a coronavirus. And we have never before seen a pandemic that can be controlled at the same time.”

When is the last time the WHO declared a pandemic?

The last time the WHO declared a pandemic was during the 2009 H1N1 swine flu, and it triggered aggressive actions, such as millions in spending to buy vaccines. But H1N1 turned out not to be as deadly and disruptive as feared, and a lot of governments were frustrated about buying vaccines that they ended up not using and harshly criticized the WHO for its declaration. Burned by that response, the WHO got rid of the six-stage procedure that led up to it declaring an influenza pandemic.

“Each time they went up a stage, it raised alarm. When they finally reached pandemic stage it caused enormous panic,” said Lawrence Gostin, a global health law professor at Georgetown University. “It was so dysfunctional and caused so much fear and panic that WHO abandoned that approach.”

The WHO’s current approach has been much more vague, essentially leaving it up to leaders to declare a pandemic when they deem it necessary.

“In many ways whether we’re in a pandemic is a semantic question,” said Alexandra Phelan, a global health lawyer at Georgetown’s Center for Global Health Science and Security.