It is official. The World Health Organization (WHO) has described the novel coronavirus as a pandemic for the first time. In a press briefing on Wednesday, WHO director-general Tedros Adhanom Ghebreyesus expressed concern about trajectory of the disease, which has rapidly expanded across the globe in the months since it was first announced in China.

Outbreaks have been reported in more than 110 countries with more than 118,000 confirmed cases and 4,200 deaths worldwide, as global stock markets continue to falter. Case counts of the coronavirus, which causes the disease named COVID-19, have risen sharply in places like Italy, Iran, and South Korea. Meanwhile, it has begun to spread across the United States as well, with more than 900 cases and 29 deaths.

“In the days and weeks ahead, we expect to see the number of cases, the number of deaths, and the number of affected countries climb even higher,” Ghebreyesus said in his announcement. “WHO has been assessing this outbreak around the clock and we are deeply concerned both by the alarming levels of spread and severity, and by the alarming levels of inaction.”

The announcement comes after weeks of speculation among officials and the news media that this emergency had already reached pandemic levels—even as public health authorities stopped just short of officially labeling it so.

So what exactly is a pandemic—and what happens when a major public health agency, like the WHO, declares one? While calling this global health crisis a pandemic might not change the facts on the ground, it can stoke public fears and propel a shift in strategy toward mitigating harm.

What is a pandemic?

Global health crises tend to grow in phases. This chain of events starts with an “outbreak”—a sudden rise in confirmed cases of an disease that’s contained to a small geographic region like Wuhan. If the disease spreads just beyond that community—like how the novel coronavirus spread across China—then it becomes an epidemic.

Pandemics, according to their classical definition, are epidemics that cross international boundaries and affect a large number of people worldwide.

“It’s all about geography,” says Lauren Sauer, an assistant professor of emergency medicine and the director of operations with the Johns Hopkins Office of Critical Event Preparedness and Response. “It’s not about severity, it’s not about high versus low case counts. It’s...do we see spread across the globe?”

Not every widespread epidemic is considered a pandemic. Seasonal influenza, for example, checks those boxes—but its cyclic nature is what differentiates it from pandemic influenza, which can spread anywhere across both hemispheres regardless of the weather. (Will warming spring temperatures slow the coronavirus outbreak?)

A pandemic declaration also takes into account who is infected and where. If a person catches the coronavirus in China and travels back to their home country, they do not count toward the tally that ultimately decides a pandemic declaration—and neither does anyone they infect. Sauer says these constraints arose out of the lessons learned during the H1N1 pandemic in 2009, when the ease of global travel made it seem like the disease was spreading faster and more widely than it was. (Here's how coronavirus spikes outside China show that travel bans aren’t working.)

Instead, public health authorities were looking for local transmission of COVID-19. That's the stage where the virus begins spreading outside of China among people who have not recently traveled to the Asian nation. Early in an epidemic, most of those cases can be traced to travelers from the outbreak's original site, in this case China. But as local transmission progresses, that contact tracing breaks down. At this turning point, the coronavirus can spread unnoticed, making it extremely difficult to control.

Some public health experts argue that the novel coronavirus achieved pandemic status weeks ago when measured against these definitions: By late February, cases had been confirmed on six continents, including 2,300 in South Korea and 650 in Italy. In many of the countries, outbreaks were being sustained locally, with U.S. examples simmering in California, Oregon, and Washington. The White House had also announced 14-day bans for any foreign nationals who have traveled through Iran, while the State Department issued its highest possible warning for travel to parts of Italy and South Korea.

So what stopped the WHO from calling this epidemic a pandemic? “In reality, it’s semantics,” Sauer says. “But semantics become important when you’re talking to the general public about these issues.”

Why pandemics do—and don’t—matter

Words matter. In a press briefing on Wednesday, director-general Ghebreyesus explained the WHO’s caution against rushing to cry “pandemic.”

“Pandemic is not a word to use lightly or carelessly,” he said. “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.”

Lawrence Gostin, a Georgetown University professor who is also director of the World Health Organization Collaborating Center on National and Global Health Law, highlights that “panic” is literally in the word “pandemic.”

In 2009, people around the world panicked when the WHO described H1N1 influenza as a pandemic, Gostin says, and then the organization was later criticized for raising public alarm when the virus turned out to not be very lethal. H1N1 now returns seasonally and is part of our annual vaccine preparations.

“So the fact that this may become a pandemic is certainly a concern because this is much more deadly than the flu,” Gostin said in an interview prior to the WHO’s announcement, “but it’s something we’ll want to delay as long as possible until we get a vaccine, which should probably be within 12 to 18 months.” (Learn about how coronavirus compares to flu, Ebola, and other major outbreaks.)

From a legal standpoint, though, it doesn’t matter whether the WHO calls this a pandemic or not.

“Describing the situation as a pandemic does not change WHO’s assessment of the threat posed by this virus,” Ghebreyesus said in the March 11 briefing. “It doesn’t change what WHO is doing, and it doesn’t change what countries should do.”

Gostin—who points out that the WHO doesn’t even actually “declare” pandemics—says the organization has already declared something far more significant: a Public Health Emergency of International Concern (PHEIC). That declaration legally allows the WHO to make recommendations on how member countries should handle an epidemic. It also mobilizes funding and political support.

So, what happens now that COVID-19 is a pandemic?

While “pandemic” might be merely a label without legal significance, it does have its value. A pandemic signifies that authorities no longer believe they can contain the spread of the virus and must move to mitigation strategies, like closing schools and canceling mass gatherings.

In his announcement—which he noted was the first time the world has seen a pandemic caused by a coronavirus—Ghebreyesus argued the disease can be controlled but acknowledged that many countries are struggling to do so because of either a lack of resources or resolve.

This is precisely why some public health experts argued for weeks that the WHO and other global agencies should go ahead and make the call, Sauer says. The sooner that public health authorities and first responders transition to mitigation measures—like the ones we see each year with the flu—the better.

In the U.S., the CDC shared its strategy for protecting communities in light of a coronavirus pandemic back in February. That strategy includes “social distancing measures” like closing schools and recommending telework to prevent infected people from spreading the disease to their classmates and colleagues. Events and mass gatherings could be postponed or even canceled. Even this summer’s Tokyo Olympics could be canceled if conditions seem too dangerous. And the CDC would advise delaying elective surgeries to ensure the availability of hospital beds.

In the weeks since, we’ve seen those social distancing measures enacted. Workplaces across the country are asking employees to telecommute and presidential candidates Joe Biden and Bernie Sanders have canceled political rallies—though President Trump announced a rally on the same day the Democratic contenders suspended their events.



Washington State has banned all events with more than 250 people in three of its counties, while Washington D.C. has declared a state of emergency and recommended the cancellation or postponement of all mass gatherings through March 31. It’s likely that public health authorities will be encouraging even more social distancing in the weeks to come now that the WHO has signaled the need to shift to mitigation.

Gostin says these social distancing measures are not something that a public health organization would recommend lightly as they impact families, communities, and economies. But Gostin says there’s one thing people really need to remember: “It’s important not to panic.”

“Kids still have to be educated, their parents still have to be able to go to work, and people want to get out and enjoy themselves as well,” Gostin says. “So it’s not something that we’d want to do. Only if it was necessary.”

Individuals can also take preventive measures of their own, including regularly washing their hands, covering their sneezes, and wiping down surfaces.

Though he acknowledged that we’ve never seen a pandemic that can be controlled, Ghebreyesus urged afflicted countries to continue to take action to suppress the spread of COVID-19.

“We cannot say this loudly enough, or clearly enough, or often enough,” he said. “All countries can still change the course of this pandemic.”