Is the Coronavirus an Epidemic or a Pandemic? It Depends on Who’s Talking

All eyes have been on the coronavirus since it crept up in Wuhan, China, in late 2019. Since then, the virus has sickened tens of thousands of people in more than three dozen countries, and its quick advance across Asia, the Middle East and Europe has raised fears that a pandemic could be on the horizon.

The World Health Organization has referred to the outbreak as an “epidemic” as opposed to a “pandemic.” But on Friday, it increased its assessment of the global risk of spread and the risk of impact of the coronavirus outbreak from “high” to “very high.”

According to the W.H.O., an epidemic is explained as a regional outbreak of an illness that spreads unexpectedly. The C.D.C. calls it “an increase, often sudden, in the number of cases of a disease above what is normally expected” in that area.

In 2010, the W.H.O. defined a pandemic as “the worldwide spread of a new disease” that affects large numbers of people. The C.D.C. says it is “an epidemic that has spread over several countries or continents, usually affecting a large number of people.”

“Typically, an outbreak becomes an epidemic when it becomes quite widespread in a particular country, sometimes in a particular region, like Zika,” Lawrence O. Gostin, a professor of global health law at Georgetown University, said on Tuesday. “Whereas a pandemic is thought to be a wide geographic spread of a disease on many parts of the world, many continents.”

Both terms are often used in reference to the coronavirus outbreak, but how they are used is subjective, and there are no hard and fast rules on when to use them, Mr. Gostin said.

Last month, the W.H.O. declared the outbreak a global health emergency. This week, Tedros Adhanom Ghebreyesus, the director-general of the W.H.O., said the decision whether to use the word “pandemic” was based on “an ongoing assessment” of the geographical spread of the virus, the severity of its effects and its impact on society.

He added: “Does this virus have pandemic potential? Absolutely, it has. Are we there yet? From our assessment, not yet.”

So far, health officials have not witnessed “the uncontained global spread” of the virus, or evidence of “large-scale severe disease or death,” Dr. Tedros said.

According to Mr. Gostin, there are two reasons Dr. Tedros stopped short of calling the outbreak a pandemic: Because the outbreak can still be contained, and to try to avoid unnecessary panic.

“He wanted to create a seriousness, a purpose, but not an overreaction,” Mr. Gostin said. “Not more travel bans. Not more closures of cities. Not more drain on human rights and economic activity.”

The Coronavirus Outbreak

  • Answers to your most common questions:

    Updated Feb. 26, 2020

    • What is a coronavirus?
      It is a novel virus named for the crownlike spikes that protrude from its surface. The coronavirus can infect both animals and people and can cause a range of respiratory illnesses from the common cold to more dangerous conditions like Severe Acute Respiratory Syndrome, or SARS.
    • How do I keep myself and others safe?
      Washing your hands frequently is the most important thing you can do, along with staying at home when you’re sick.
    • What if I’m traveling?
      The C.D.C. has warned older and at-risk travelers to avoid Japan, Italy and Iran. The agency also has advised against all nonessential travel to South Korea and China.
    • Where has the virus spread?
      The virus, which originated in Wuhan, China, has sickened more than 80,000 people in at least 33 countries, including Italy, Iran and South Korea.
    • How contagious is the virus?
      According to preliminary research, it seems moderately infectious, similar to SARS, and is probably transmitted through sneezes, coughs and contaminated surfaces. Scientists have estimated that each infected person could spread it to somewhere between 1.5 and 3.5 people without effective containment measures.
    • Who is working to contain the virus?
      World Health Organization officials have been working with officials in China, where growth has slowed. But this week, as confirmed cases spiked on two continents, experts warned that the world was not ready for a major outbreak.