What is a pandemic? How coronavirus compares to recent health outbreaks

What is a pandemic? How is it different than an epidemic?

As coronavirus cases continue to spread, a look at previous pandemics and epidemics

The new coronavirus, which causes COVID-19, continues to spread worldwide, with more than 118,000 cases reported worldwide, according to the World Health Organization.

On Wednesday, health officials from World Health Organization officially labeled the outbreak a “pandemic.”


"This is not just a public health crisis, it is a crisis that will touch every sector," Dr. Tedros Adhanom Ghebreyesus, WHO director-general, told media outlets. "So every sector and every individual must be involved in the fights."

So what exactly is a pandemic? Here’s what health officials say and a look back at some recent examples.

What is a pandemic?

The CDC has not released a coronavirus-specific pandemic definition but has said "Guidance and tools developed for pandemic influenza planning and preparedness can serve as appropriate resources for health departments in the event the current COVID-19 outbreak triggers a pandemic."

The center's definition of flu pandemics is  "Pandemics happen when new (novel) influenza A viruses emerge which are able to infect people easily and spread from person to person in an efficient and sustained way. Because the virus is new to humans, very few people will have immunity against the pandemic virus, and a vaccine might not be widely available."

The CDC notes that the new virus will make a lot of people sick. Just how sick people gets depends on the specific characteristics of the virus, whether there is any built up immunity and how the age of the person infected.

The WHO defines a pandemic as "the worldwide spread of a new disease." The organization notes that past pandemics have typically originated from animal influenza viruses.

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What is the difference between pandemic, epidemic and endemic diseases?

Pandemics have more to do with how widespread geographically a disease becomes, especially when it crosses international borders, according to the WHO.  While epidemics occur when a higher number of people than usual in a given country or region experience an infection, according to the CDC.

There are also endemic diseases, which refers to a disease or infection that is consistently present in a geographic area, according to the CDC.

How common are pandemics?

The CDC notes that influenza pandemics are rare. There were only three instances of pandemic flu in the 20th century, according to the CDC.

"Although pandemics occur infrequently, planning and preparing for a pandemic is important to ensure an effective response," the CDC notes.

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What are some recent examples of pandemics?

Many past pandemics have been tied to influenza. The CDC notes that the coronavirus "is a respiratory disease that seems to be spreading much like flu."

In 1918, a H1N1 pandemic killed an estimated 500 million people worldwide and 675,000 people in the United States, according to the CDC.

In 1957-58, a H2N2 pandemic killed an estimated 1.1 million people worldwide and 116,000 people in the United States, CDC data shows.

A 1968 pandemic of the influenza virus H3N2 killed more than 1 million people worldwide and 100,000 people in the U.S. Most of the deaths affected people 65 years and older, the CDC says.

Most recently, a 2009 strand of H1N1 affected mostly young kids and middle-aged adults. The CDC estimates there were 60 million cases of in the 2009 pandemic, with more than 12,000 deaths in the United States. In 2010, WHO declared an end to the pandemic, although the H1N1 strand continues to circulate seasonally and cause deaths annually.

How does pandemic flu differ from other flu seasons?

The seasonal flu tend to peak between December and February. People tend to have some built up immunity from previous exposure and flu vaccines. The CDC notes that the seasonal flu can have varying levels of impact, but typically there are only certain people at high-risk for serious complications, like elderly populations, pregnant women and infants. The CDC estimates that flu-related deaths from 2010-2019 ranged from 12,000 to 56,000, while hospitalizations from the flu are estimated between 140,000-810,000 cases.

The CDC reports that the 2017-2018 flu season was the worst in the last decade, with about 45 million Americans showing some symptoms.

On the other hand, pandemic flu seasons are rare. For example, the CDC says the estimated death toll in the U.S. during the 1918 pandemic was about 675,000 people. Pandemic flu seasons put otherwise healthy people at risk, because there is little to no immunity built up and no previous exposure to the virus or similar viruses.

What are examples of recent epidemics?

While they didn't rise to pandemic levels, some recent examples of epidemics include the 2014 Ebola outbreak, which had more than 28,600 cases and resulted in 11,325 deaths, according to the CDC.

In 2003, a SARS outbreak affected about 8,100 people worldwide and about 775 people died, according to CDC data. In 2012, a break out of MERS, or Middle East Repository Syndrome began to spread, including two unlinked cases in the United States. Both were hospitalized and later discharged, according to the CDC. Worldwide, there have been about 2,500 cases and more than 860 deaths since 2012, according to WHO.


CDC recommends preventive actions to help prevent the spread of respiratory diseases:

• Avoid close contact with people who are sick.

• Avoid touching your eyes, nose, and mouth.

• Stay home when you are sick.

• Cover your cough or sneeze with a tissue, then throw the tissue in the trash.

• Clean and disinfect frequently touched objects and surfaces using a regular household cleaning spray or wipe.

• CDC does not recommend that people who are well wear a facemask to protect themselves from respiratory diseases, including COVID-19. Facemasks should be used by people who show symptoms of COVID-19 to help prevent the spread of the disease to others. The use of facemasks is also crucial for health workers and people who are taking care of someone in close settings (at home or in a health care facility).

• Wash your hands often with soap and water for at least 20 seconds, especially after going to the bathroom; before eating; and after blowing your nose, coughing, or sneezing. If soap and water are not readily available, use an alcohol-based hand sanitizer with at least 60% alcohol. Always wash hands with soap and water if hands are visibly dirty.

• If you are concerned you might have the coronavirus, call your healthcare provider before going to a hospital or clinic. In mild cases, your doctor might give you advice on how to treat symptoms at home without seeing you in person, which would reduce the number of people you expose. But in more severe cases an urgent care center or hospital would benefit from advance warning because they can prepare for your arrival. For example, they may want you to enter a special entrance, so you don’t expose others.

Source: CDC


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