Pandemic 101: Understanding the basics

Full series

By Philip Smith, assistant professor of kinesiology and health, and Shavon Anderson, university communications and marketing 


Philip Smith, assistant professor of kinesiology and health.

As COVID-19 continues to spread across the United States and the world, many communities have lingering questions about the deadly virus and its impact. To help address concerns, Miami’s office of university news and communications connected with Philip Smith, assistant professor of kinesiology and health. Smith has expertise in psychology, epidemiology, health policy, community health and health behavior. In part 1 of a 4-part series, Smith breaks down the basics of an epidemic in a way that’s easy to understand, in his own words.

Endemic, epidemic and pandemic

An “endemic” means there is an infectious disease in a population, but it’s expected. People get sick and die from it, and cases fluctuate year to year. In the U.S., your typical increase in people with the flu during flu season is an example of something that is endemic.

An “epidemic” is when – in any population, like the U.S. –– you have many more infections from something than you expect. It could be something new that is getting people sick, or it could be something that typically gets people sick. Either way, you have many more cases than normal. Think back, for example, to Zika virus. In 2015, we hadn’t really encountered problems with the virus before, and then all of a sudden we had a large number of people getting sick. This is an epidemic.

A “pandemic” is an epidemic that includes countries across the world. This is our current situation with COVID-19. Back in December, we weren't expecting so many people to get sick. Then, there was a huge spike in China (epidemic), which spread to other countries (pandemic).

Why it matters: breaking down disease

In the case of a virus, if it’s expected –– like the endemic flu –– our health care providers are ready and prepared to deal with it. There are also more tools, like vaccines and treatments, that have been developed. When something is epidemic or pandemic, our healthcare providers can become overwhelmed. COVID-19 is particularly worrisome because of how fast it spreads.

Epidemiology uses a very basic idea to visualize disease: a triangle. One point is a virus, bacteria or something else that gets people sick. The second point is the host, or the person who gets sick. The third point is the environment in which the host interacts with the virus, bacteria, etc. Sometimes in the middle of the triangle is an animal or insect that carries the bacteria or virus. All of these things are connected. Any one of these things can change, or multiple of these things can change, in a way that creates an epidemic or pandemic. 

In the case of COVID-19, it isn’t known exactly what happened and why it didn’t happen before. It is possible that the virus changed in such a way that it made it more contagious for humans. The virus could have changed in a way that made it more likely to be spread from animals to humans. But when you think about the host (humans), no one has immunity. 

When you look at the environment, there are worse outbreaks in places like New York City, which has a high international population and densely crowded communities. Just as changes in a virus can increase its spread, changes can also cause pandemics to cease. A virus may change in a way that it becomes less contagious among humans, more humans might develop immunity, or humans start social distancing.

Follow Miami's office of university news and communications for continuing coverage of the coronavirus pandemic.