Coronaviruses are a large family of viruses that usually cause mild to moderate upper-respiratory tract illnesses, like the common cold, in people. However, three times in the 21st century coronavirus outbreaks have emerged from animal reservoirs to cause severe disease and global transmission concerns.

There are hundreds of coronaviruses, most of which circulate among animals including pigs, camels, bats and cats. Sometimes those viruses jump to humans—called a spillover event—and can cause disease. Seven coronaviruses are known to cause human disease, four of which are mild: viruses 229E, OC43, NL63 and HKU1. Three of the coronaviruses can have more serious outcomes in people, and those diseases are SARS (severe acute respiratory syndrome) which emerged in late 2002 and disappeared by 2004; MERS (Middle East respiratory syndrome), which emerged in 2012 and remains in circulation in camels; and COVID-19, which emerged in December 2019 from China and a global effort is under way to contain its spread. COVID-19 is caused by the coronavirus known as SARS-CoV-2.

Coronaviruses are named for the crown-like spikes on their surface. There are four main sub-groupings of coronaviruses, known as alpha, beta, gamma, and delta.

Human coronaviruses were first identified in the mid-1960s. The seven coronaviruses that can infect people are:

Common human coronaviruses

1. 229E (alpha coronavirus)
2. NL63 (alpha coronavirus)
3. OC43 (beta coronavirus)
4. HKU1 (beta coronavirus)

Other human coronaviruses

1. MERS-CoV (the beta coronavirus that causes Middle East Respiratory Syndrome, or MERS)
2. SARS-CoV (the beta coronavirus that causes severe acute respiratory syndrome, or SARS)
3. SARS-CoV-2 (the novel coronavirus that causes coronavirus disease 2019, or COVID-12)

People around the world commonly get infected with human coronaviruses 229E, NL63, OC43, and HKU1.

Sometimes coronaviruses that infect animals can evolve and make people sick and become a new human coronavirus. Three recent examples of this are 2019-nCoV, SARS-CoV, and MERS-CoV.

Research evidence suggests that SARS-CoV and MERS-CoV originated in bats. SARS-CoV then spread from infected civets to people, while MERS-CoV spreads from infected dromedary camels to people. To date, the origin of SARS-CoV-2 which caused the COVID-19 pandemic has not been identified. The scientific evidence thus far suggests that SARS-CoV-2 likely resulted from viral evolution in nature and jumped to people or through some unidentified animal host. Public health and scientific organizations are engaged in a continued international effort to uncover the origins of SARS-CoV-2, which is essential to preventing future pandemics.

SARS-CoV-2 and NIAID-Supported Bat Coronavirus Research

Unfortunately, because the origins of the SARS-CoV-2 have not yet been identified, misleading and false allegations have been made about NIAID-supported research on naturally occurring bat coronaviruses. Specifically, these allegations have targeted research conducted at the Wuhan Institute of Virology in Wuhan, China, funded through a subaward from NIAID grantee EcoHealth Alliance. The naturally occurring bat coronaviruses studied through this subaward were significantly, genetically different from SARS-CoV-2 and, therefore, could not have caused the COVID-19 pandemic. For a detailed, scientific analysis as to why this is the case, please see: SARS-COV-2 and NIAID-Supported Bat Coronavirus Research.

Spike protein key to vaccine development

The genetic blueprint material for SARS-CoV-2 is called RNA (yellow spirals). The RNA contains information to specify the amino acids that make up the proteins, which are the actual building blocks for the virus particle.

The RNA is protected in the virus envelope (black outer ring) until a potential host cell is found. The envelope is made up of several proteins, including envelope protein (blue spikes); membrane protein (yellow spikes); and spike glycoprotein or spike protein (red, tall spike).

The spike glycoprotein helps the virus latch onto and gain entry into the host cell, so that the virus can infect the cell.