Epidemic and pandemic are used to describe widespread outbreaks of a disease, but there are subtle differences between the two words.

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Epidemic versus Pandemic comparison chart
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Definition An epidemic occurs when the incidence rate (i.e. new cases in a given human population, during a given period) of a certain disease substantially exceeds what is "expected," based on recent experience. A pandemic is an epidemic of an infectious disease that spreads through human populations across a large region, like a continent.
Comparison Disease outbreak that is concentrated in a particular region. Disease outbreak that occurs over a wide geographic area and affects a very high proportion of the population.


An epidemic (from Greek epi- upon + demos people) is a classification of a disease that appears as new cases in a given human population, during a given period, at a rate that substantially exceeds what is "expected," based on recent experience (the number of new cases in the population during a specified period of time is called the "incidence rate").

A pandemic (from Greek πᾶν (pan, “all”) + + δῆμος (dēmos, “the people”) is an epidemic that spreads across a large region (for example a continent), or even worldwide.

Differences Between an Epidemic and a Pandemic

Simply put, when an epidemic gets out of hand, it is called a pandemic. This has 2 nuances:

Video Explaining the Differences

In this video, Dr. Kenneth Alexander, chief of pediatric infectious diseases at the University of Chicago Medical Center, explains the differences between an outbreak, an epidemic, and a pandemic, and answers questions about the swine flu outbreak.

Flu Pandemic

Experts warn that a new flu pandemic could kill 20 million people globally.[1] There have been multiple flu pandemics in the 20th century. The Spanish flu pandemic of 1918 is estimated to have caused 50 million deaths, with anywhere from 20% to 40% of the world's population falling sick. The Asian flu pandemic of 1958–59 resulted in the death of about 2 million people and the Hong Kong flu of 1968–69 is estimated to have caused around 1 million deaths.

The only effective mitigation against a pandemic is a vaccine. Scientific advances have considerably shortened the time it takes to develop a new vaccine. However, it is still estimated to be around 30 weeks. Experts believe that shortening this to 6 weeks is the only way to curb the spread of a pandemic.

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"Epidemic vs Pandemic." Diffen.com. Diffen LLC, n.d. Web. 21 Feb 2019. < >