Coronaviruses have been infecting humans for at least several centuries, and the virus family itself likely dates back millions of years. The first human coronavirus was identified in 1965, but genetic evidence shows these viruses were jumping from animals to people long before scientists had the tools to detect them.
The Virus Family Is Ancient
Coronaviruses are far older than most people realize. Molecular clock analyses, which estimate how long ago viruses diverged from a shared ancestor based on their rate of genetic change, initially placed the common ancestor of all coronaviruses at roughly 10,000 years ago. But a 2013 study in the Journal of Virology argued that this was a dramatic underestimate. When researchers accounted for natural selection pruning mutations over deep time, they calculated the true common ancestor may have existed around 293 million years ago, with a range of 190 to 489 million years. That lines up with fossil and molecular evidence for when mammals and birds first split from each other, which matters because different branches of the coronavirus family infect these two groups of animals separately.
In other words, coronaviruses have likely been co-evolving alongside their animal hosts for hundreds of millions of years. The versions that infect humans are just a tiny, recent branch of a very old family tree.
When Coronaviruses Started Infecting Humans
Two of the four “common cold” coronaviruses have enough genetic data to estimate when they first jumped into human populations. One strain, originally discovered in the 1960s, appears to have split from a bovine (cow) coronavirus lineage around 1923, with estimates ranging from 1872 to 1967. Another strain separated from a camel coronavirus sometime in the 18th century, likely around 1754. Since cows and camels are plausible sources for these spillover events, those dates represent reasonable estimates for when these viruses first began circulating in people.
That means humans have been catching coronaviruses for at least a couple of hundred years, and possibly much longer. These older strains now cause roughly 15 to 30 percent of common colds and are so widespread that most people get infected with at least one of them during childhood.
The 1960s: Scientists Finally Spot Them
The first human coronavirus was described in The BMJ in 1965. Researchers worked from a nasal swab taken from a boy with a typical common cold in 1960, then confirmed the virus could cause colds by inoculating volunteers with the sample. When they examined the virus under an electron microscope, they noticed a distinctive fringe of club-shaped projections surrounding the particle, resembling the corona (or crown) of the sun. In 1968, a group of virologists writing in the journal Nature formally proposed the name “coronavirus” for this new group.
Four common human coronaviruses have been identified since that era. Two are alpha coronaviruses (strains 229E and NL63) and two are beta coronaviruses (OC43 and HKU1). All four cause mild upper respiratory infections in most people.
SARS, MERS, and COVID-19
The picture changed dramatically in the 2000s, when three additional coronaviruses emerged that could cause severe illness.
- SARS (2002 to 2004). A beta coronavirus caused an epidemic of severe acute respiratory syndrome that spread to more than two dozen countries from late 2002 to late 2003. The outbreak was contained through aggressive quarantine measures and burned out without a vaccine.
- MERS (2012 to present). First reported in 2012, this beta coronavirus causes Middle East respiratory syndrome. It continues to cause sporadic cases, primarily in the Arabian Peninsula, but has never sustained widespread human-to-human transmission.
- SARS-CoV-2 (2019 to present). On December 31, 2019, the WHO’s office in China was notified of a cluster of pneumonia cases of unknown cause in Wuhan, with initial cases linked to a seafood market. The virus was identified as a new beta coronavirus in early January 2020 and went on to cause the COVID-19 pandemic.
Why “New” Coronaviruses Keep Appearing
Coronaviruses have an unusually large genome for an RNA virus, which gives them more genetic flexibility. They also recombine readily, meaning two different coronavirus strains infecting the same animal cell can swap chunks of genetic material and produce novel combinations. This is one reason coronaviruses periodically jump from bats, camels, cows, or other animals into humans. The four mild strains circulating today almost certainly started as animal viruses that crossed over and gradually adapted to spread easily among people. SARS, MERS, and COVID-19 represent more recent jumps where the virus retained the ability to cause serious disease.
So while COVID-19 feels new, the coronavirus family has been part of human life for centuries and part of life on Earth for far longer. The seven strains known to infect humans are simply the ones that have successfully made the leap from animals, with new spillover events an ongoing possibility rather than a one-time event.