Coronaviruses are a large, diverse group of viruses that may cause diseases in humans and other animals. Although experts first identified coronaviruses in the mid-1900s, they have likely existed for thousands of years.

These viruses most commonly affect cats, bats, pigs, and camels. However, some coronaviruses can evolve to cause infections in humans.

Although “coronavirus” often has associations with the SARS-CoV-2 virus that caused the COVID-19 pandemic, many different coronaviruses exist. Many never have the ability to cause infections in humans, and the viruses vary in terms of how contagious and harmful they are.

Read more to learn about how researchers discovered coronaviruses, how they have evolved, and what scientists expect in future coronaviruses.

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A doctor cares for a suspected SARS victim April 14, 2003 at Tan Tock Seng hospital in Singapore. Luis Enrique Ascui/Getty Images

Some say researchers first discovered coronaviruses in the mid-1960s. Other sources report identifying coronaviruses as early as 1937.

However, like many viruses, coronaviruses have been circulating in human populations for thousands of years. While it is impossible to know just how old they are, coronaviruses have likely been around far longer than humans have known about them.

Some research has investigated historic coronaviruses.

In a 2021 study, researchers looked at genomic data from 2,500 modern humans. This data showed that an ancient form of coronavirus existed more than 20,000 years ago in what is now East Asia.

Medical students at the University of Chicago discovered the first coronavirus known to affect humans. Formally called HCoV-229E, experts know it as 229E.

Much like the common cold, 229E is a mild-to-moderate upper respiratory illness. Many people will have it or another similar coronavirus in their lifetime and never know it.

The first coronavirus to cause widespread illness in humans in modern history is SARS-CoV. Likely originating in bat populations, experts first discovered it in 2002, and it went on to affect over 8,000 people in 29 countries.

However, the SARS outbreak was not widespread enough for health officials to consider it a pandemic. The first coronavirus that received pandemic classification was the SARS-CoV-2 virus that caused the ongoing COVID-19 pandemic.

Of the hundreds of viruses in the coronavirus family, the majority cause mild-to-moderate respiratory illnesses that share similarities to the common cold.

There are seven types of coronavirus known to cause illness in humans:

  • 229E (alpha coronavirus)
  • NL63 (alpha coronavirus)
  • OC43 (beta coronavirus)
  • HKU1 (beta coronavirus)
  • MERS-CoV
  • SARS-CoV
  • SARS-CoV-2

In the past two decades, some coronaviruses have evolved in animal species to the point where they can cause infections in humans. This is called a “spillover event.”

The human immune system is not familiar with these viruses, so they tend to cause serious illness and spread easily.

Three species of coronavirus can cause serious and sometimes even fatal infections:

  • SARS-CoV
  • MERS
  • SARS-CoV-2


Commonly referred to as SARS, health experts first identified this virus in Southern China in November 2002.

Since 2004, there have been no reported human cases of SARS infections. However, the virus is likely still in existence to some extent.

During the SARS outbreak, the illness had a 9.6% mortality rate.


Researchers identified the next species of coronavirus to cause major disease in Saudi Arabia in September 2012. They called it MERS-CoV (Middle East Respiratory Syndrome coronavirus), or MERS.

Although it is less common now, MERS continues to cause sporadic, localized outbreaks in some parts of the world, primarily the Arabian Peninsula. As of 2019, only two infections affected people living in the United States, both of which occurred in 2014.

The mortality rate associated with MERS infections is 35%. However, this number may be inaccurate because of a lack of case documentation.


Some researchers think SARS-CoV-2, which causes the disease COVID-19, first evolved to cause human infections in China around December 2019. However, this may simply be the first place where researchers identified the infection from the virus.

On March 11, 2020, the World Health Organization (WHO) declared COVID-19 a global pandemic. This means it was causing widespread global illness.

Although the precise source of SARS-CoV-2 remains unknown, some early experts think it may have started in bats.

While its associated disease COVID-19 has a lower mortality rate than SARS and MERS, SARS-CoV-2 is also more contagious. According to current estimates, the currently circulating coronavirus has undergone around a hundred different mutations so far.

The CDC has identified the Delta and Omicron strains as variants of concern. As of January 2022, the Omicron variant has caused more than 96% of COVID-19 cases in the United States.

According to what researchers currently know, SARS-CoV-2 appears to have first caused infections in humans in Wuhan, the capital of the Hubei province in China.

However, the exact source of SARS-CoV-2 remains unknown.

From an evolutionary perspective, it is in a virus’s best interest to become less deadly and more contagious. This is what the SARS-CoV-2 variant, Omicron, seems to be doing.

The ultimate goal of a virus is to replicate and circulate as many copies of its RNA, or genes, as possible.

This means that in most cases, the virus does not want to kill or cause severe illness in its host, as doing so limits its ability to reproduce and spread.

In an ideal world for most viruses, they will cause infections that do not interfere with someone’s ability to go out and spread the virus as much as possible, or even better, cause no noticeable symptoms at all.

There are instances in history of viruses evolving to become less dangerous. For example, the H1N1 influenza virus associated with the 1918 “Spanish flu” later became the far less deadly 2009 “swine flu.”

Therefore, when considering how SARS-CoV-2 will evolve, experts think it makes evolutionary sense for the virus to become less deadly and more contagious. However, this does not mean it will. Viruses are unpredictable, and it is impossible to know what a new strain of SARS-CoV-2 or new virus will bring.

Although experts first identified coronaviruses in the mid-1900s, they have likely been circulating in human populations for thousands of years.

Many coronaviruses are relatively harmless and cause mild-to-moderate respiratory symptoms. However, some coronaviruses, such as SARS, MERS, and SARS-CoV-2, have a greater impact on populations.

It is impossible to know how future coronaviruses will affect humans, but they will likely become more contagious and less harmful over time.