Coronaviruses are a family of viruses that cause illness in animals and humans. They can cause upper respiratory tract infections in humans, with symptoms and complications ranging from mild to severe.
Most species of coronavirus do not affect humans. So far, seven coronaviruses have caused illness in humans — including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 19 (COVID-19).
In this article, we explore what coronaviruses are and how different types affect humans.
All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.
Coronaviruses are a large family of viruses that cause upper respiratory tract and intestinal illness.
The name “coronavirus” comes from the crown-like spikes that cover the surfaces of the viruses in this family. Coronam is Latin for “crown.”
Most coronaviruses affect animals, such as bats and pigs. Seven coronaviruses have spread to humans.
There are four subtypes of coronavirus — alpha, beta, gamma, and delta —and scientists use these classifications to categorize the various species.
Among all the coronaviruses, seven have affected humans. Four of these are common and cause mild illnesses in the upper and lower airways, nose, sinuses, throat, and lungs.
The remaining three can cause more severe illness. They are:
- severe acute respiratory syndrome coronavirus (SARS-CoV), which led to the SARS epidemic in 2002–2003
- Middle East respiratory syndrome coronavirus (MERS-CoV), which caused an outbreak of MERS that began in 2012
- SARS-CoV-2, the virus responsible for the COVID-19 pandemic
Common human coronaviruses
These four coronaviruses typically cause mild respiratory illnesses, such as the common cold, in humans. They are:
These viruses are common worldwide and account for around 15–30% of all common colds. They rarely spread to the lower respiratory tract.
This virus causes severe acute respiratory syndrome, or SARS. The first cases of this disease in humans occurred in the Guangdong province of China in 2002.
In total, SARS spread across 26 countries, causing an epidemic with more than 8,000 cases. Since 2004, there have been no recorded cases of SARS in humans.
The symptoms of SARS include:
In severe cases, SARS causes a lack of oxygen in the blood, leading to death in 10% of people.
A 2019 report from the World Health Organization (WHO) suggests that MERS-CoV may spread through contact with animals, particularly camels. Human-to-human transmission is also possible during close contact with people who are sick. Healthcare workers, for example, may be particularly vulnerable.
- a fever
- a cough
- shortness of breath
Since 2012, most cases of MERS have occurred in the Middle East. There have been 2,494 cases and 858 deaths.
No vaccines or drugs can treat or prevent MERS, and health authorities continue to monitor the virus closely.
SARS-CoV-2 is the virus that causes COVID-19. The first cases of COVID-19 were identified in the city of Wuhan, China, in 2019.
The illness can cause mild to severe symptoms. People with underlying medical conditions and older adults are most at risk of severe COVID-19.
Common symptoms include:
- a fever
- a cough
- difficulty breathing
- body aches
- a new loss of taste or smell
- a sore throat
- nausea and vomiting
Not everyone with COVID-19 develops all of these symptoms — a person may only have one or two. Also, some people with the disease experience very mild symptoms, while others experience none at all.
Doctors are still learning the best ways to treat COVID-19. Meanwhile, the European Medicine Agency has endorsed the use of dexamethasone for people who need oxygen or ventilation and the Food and Drug Administration (FDA) have also authorized the use of remdesivir for people requiring hospital care.
Major multinational efforts are underway to develop a vaccine to prevent infections causing COVID-19.
Coronaviruses reach humans through contact with animals. This includes animals such as livestock, including camels, and others, such as bats and cats.
Occasionally, one of these coronaviruses evolves the ability to infect humans.
Coronaviruses and influenza, or flu, viruses can both cause upper respiratory tract infections, and both can spread through close contact.
They also tend to cause similar symptoms, including a cough, a fever, and tiredness.
However, there are some important differences between flu viruses and the newest coronavirus to infect humans, SARS-CoV-2.
SARS-CoV-2 has a higher risk of causing severe illness and death than influenza viruses. It also has a longer incubation period and is transmissible for 2 days before, and at least 10 days after, symptoms appear.
However, the flu is more likely to cause complications in children, while COVID-19 generally appears to have less severe effects in children than in adults.
Until scientists develop vaccines for coronaviruses such as SARS-CoV-2, the most effective way to prevent transmission is so to follow official guidelines about physical distancing and hygiene.
According to the Centers for Disease Control and Prevention (CDC), the best ways to avoid the novel coronavirus involve:
Wash the hands often, for at least 20 seconds at a time, with soap and water. This is especially important:
- after visiting a public place
- after coughing, blowing the nose, or sneezing
- before preparing or eating food
- after using the bathroom or changing a diaper
- after handling a face mask
- after taking care of someone who is unwell
- after touching animals or pets
If soap and water are not available, use alcohol-based hand sanitizer, which should contain at least 60% alcohol.
Stay 6 feet, or 2 meters, away from people outside the household wherever possible. At home, avoid close contact with people who are sick.
Wear a mask that covers the nose and mouth in public and when socializing with people outside the household.
Household and personal hygiene
Every day, it is important to clean and disinfect surfaces that people touch frequently. This includes phones, door and cupboard handles, toilets, faucet knobs, and tables.
First, clean the surfaces with soap and water. Then, use a household disinfectant.
Another key element of hygiene involves covering coughs and sneezes with the inside of the elbow, rather than the hands, and avoiding touching the face unnecessarily.
Anyone who may have symptoms of COVID-19 should stay home and call a doctor. Do not visit a medical facility in person or spend any time in public areas.
To any extent possible, stay away from other household members and pets, and wear a mask, even at home. Most people with COVID-19 recover at home without the need for medical treatment.
Call 911 or otherwise contact emergency services if any of the following occur:
- trouble breathing
- persistent pain or pressure in the chest
- a seeming inability to wake up or stay awake
- a bluish tinge to the lips or face
Let the emergency services staff know before they arrive that COVID-19 is a possible cause of the symptoms, so they can take proper precautions.
Seven viruses in the coronavirus family infect humans. Most cause mild respiratory infections, such as the common cold. Three of these viruses cause more severe illness, and one example is SARS-CoV-2, which causes COVID-19.
There are currently no proven treatments for COVID-19, but health authorities and researchers are working hard to find viable options.