What's the Difference Between an Epidemic and Pandemic?

Vanessa Caceres
·7 min read

With all the focus on the new coronavirus disease, COVID-19, you may hear some confusing and even misused terms. Epidemic and pandemic are just two of the words used frequently in news stories about the disease. They're not the same thing.

What Is an Epidemic?

An epidemic is a rise in the number of cases of a disease beyond what is normally expected in a geographical area, according to the Centers for Disease Control and Prevention. Frequently, the rise in cases happens quickly.

"It boils down to incidences and increases in certain areas," says Dr. Manish Trivedi, director of the Division of Infectious Diseases at AtlantiCare Regional Medical Center in Galloway, New Jersey.

For example, some areas may have a sudden spike in flu cases when the flu is prevalent. However, that increase in cases doesn't spread among all countries and continents. It may not even spread across an entire state.

[SEE: What You Really Need to Know About Coronavirus.]

Epidemics happen frequently, but many people aren't familiar with them unless they're directly affecting their home region, Trivedi says. A few examples of epidemics include:

-- The Zika virus outbreak that occurred in 2016 and 2017. Zika is spread by mosquitoes in tropical areas and in travelers returning from those areas. Although most people have mild or no symptoms when they contract Zika, the virus can cause microcephaly, a serious birth defect, in women who are pregnant. In 2016, there were 5,168 cases with symptoms reported in the U.S., according to the CDC. By 2019, there were only 19 reported cases in the U.S.

-- The Ebola outbreak that occurred in 2014 to 2016 in West Africa was the largest outbreak of the disease, the World Health Organization reports. (The Ebola virus was originally discovered in 1976 in what is now the Democratic Republic of Congo.) The 2014 to 2016 epidemic began in Guinea and moved to Sierra Leone and Liberia. There also was an outbreak in the Democratic Republic of Congo in 2018/2019. Ebola can frequently kill if it's not treated. A total of 28,600 cases and 11,325 deaths took place from Ebola in 2014 to 2016, the CDC reports.

-- The severe acute respiratory syndrome (SARS) virus that spread in Asia beginning in 2003 was an epidemic. SARS is part of the coronavirus family of diseases. Around the world, 8,098 people became sick from SARS and 774 died. Although SARS did spread outside of Asia, it was associated with travel from the affected countries.

-- Flu epidemics. Some areas of the U.S. (or other countries) may experience a flu epidemic if the number of cases rises beyond the norm. Trivedi's hospital did not experience a flu epidemic this most recent flu season, but they did see a rise in cases -- by as much as 2% during one week alone in January. Among those with the flu, 73% had not received a flu vaccine. "That's not an epidemic, but it became larger scale," Trivedi says. "It could become an epidemic." Epidemics can be avoided when people practice safe hygiene such as washing their hands and staying home when sick.

For an epidemic to stop, the number of cases needs to go down. This is often tied into stopping how it's transmitted.

[SEE: How Does the Coronavirus Affect Children and Infants?]

What Is a Pandemic?

A pandemic is used to describe a disease that has spread across many countries and affects a large number of people. Neither the CDC nor the WHO specify how many countries or how many people need to be affected in order for something to be declared a pandemic.

"We assume with a pandemic that everyone can be potentially exposed," says Dr. Andres Romero, an infectious disease specialist at Providence Saint John's Health Center in Santa Monica, California.

Before a disease becomes a pandemic, it has to reach a few other levels, says Rodney Rohde, who is an honorary professor of international studies and associate director for the Translational Health Research Initiative at Texas State University in San Marcos, Texas.

Here are those levels, in increasing severity, according to the CDC:

-- Sporadic, used to describe when a disease is happening infrequently and irregularly.

-- Endemic, or something that's a constant presence in a geographic area. For instance, there are tropical parts of the world where the mosquito-borne infection malaria is endemic.

-- Epidemic, which is a sudden increase in the number of cases and is more than what's expected for an area.

-- Finally, there's pandemic, such as COVID-19.

Some previous examples of pandemics include:

-- The Spanish flu (H1N1 virus) of 1918. (Fans of the "Twilight" series may remember that Edward Cullen almost died during the Spanish influenza pandemic.) About 500 million people -- a third of the population around the globe -- were sick from the Spanish flu. A total of 50 million people or more died from it around the world, according to the CDC. The first people identified with it in the U.S. were military personnel.

-- In 1968, there was a pandemic caused by an influenza A (H3N2) virus that killed a million people worldwide, including 100,000 in the U.S. There have been other flu pandemics in the past century, including the H1N1 pandemic in 2009. Although the WHO declared an end to the H1N1 pandemic in August 2010, the virus still circulates seasonally during flu season.

A pandemic may sound scarier than an epidemic, but it all depends on where you live. "A pandemic is more concerning for the world, but if you live where there is an epidemic going on, that's just as concerning for you," says Dr. Shira Doron, hospital epidemiologist at Tufts Medical Center and an associate professor at Tufts University in Boston.

You also may be concerned about both an epidemic and a pandemic if you live with a pre-existing condition, such as diabetes or COPD, that could make you more vulnerable to get a contagious infection.

Just like with an epidemic, a pandemic is over when the high number of cases diminishes. Making the decision to say that a pandemic is no longer present can be difficult. "I empathize with the WHO, CDC and others who are working during difficult times while trying to hit a constantly moving target," Rohde says.

[SEE: Why You Must Stay Home When You Have the Flu.]

Is the New Coronavirus an Epidemic or Pandemic?

COVID-19 is now a pandemic, as WHO director-general Tedros Adhanom Ghebreyesus declared during a media briefing on Wednesday, March 11. The decision to declare a pandemic is not one made lightly, Ghebreyesus added.

As of March 12, there are more than 118,000 cases in 114 countries; and nearly 4,613 people have died from it, according to the WHO. More than 90% of the cases are in four countries -- China, South Korea, Italy and Iran -- two of which (China and South Korea) have declining numbers of cases. There are 77 countries with no cases; 55 countries have 10 cases or less.

On Monday, March 9, Ghebreyesus said that the threat of a pandemic was "very real," but had not yet called it a pandemic.

Decisions made by governments, businesses, communities, families and individuals can change and influence what happens with the new coronavirus disease, he adds. "If countries detect, test, treat, isolate, trace and mobilize their people in the response, those with a handful of cases can prevent those cases (from) becoming clusters, and those clusters (from) becoming community transmission," Ghebreyesus says.

Doron echoes some of Ghebreyesus's sentiments. "Referring to this epidemic as a pandemic should not be interpreted as implying that COVID-19 is a bad pandemic, or that widespread fatalities are expected," Doron says.

For the most up-to-date information on the new coronavirus disease, check with the CDC, WHO, and your local department of health, Romero advises.

Vanessa Caceres began writing for U.S. News in 2017, originally specializing in diabetes. She's a nationally published health, travel and food writer with an undergraduate degree in journalism and psychology from Hampshire College in Amherst, Massachusetts, and a graduate degree in linguistics/bilingual education from Georgetown University in Washington, D.C. In addition to U.S. News, Vanessa's health writing has been published with Everyday Health, Self, Newsday HealthLink, EyeWorld, The Rheumatologist and various other publications. She is a member of Business Networking International (BNI). Connect with her on Twitter at @FloridaCulture.