Coronaviruses (abbreviated CoVs) are a family of enveloped, positive-sense single-stranded RNA viruses that infect both humans and animals. Coronaviruses got their name because their outer proteins look like a crown ("corona" means crown in Latin). There are four main subgroups of coronaviruses: alpha, beta, gamma, and delta.
Coronaviruses that can infect humans (called human coronaviruses) were first identified in the mid-1960s. There are seven known human coronaviruses: four common types—229E, NL63, OC43, and HKU1—and three severe types—Middle East respiratory syndrome (MERS)-CoV; severe acute respiratory syndrome (SARS)-CoV; and the 2019 novel coronavirus (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19). Infection with the four common coronaviruses is common worldwide, especially in young children and during cold and flu season.
Most viruses in general have animal reservoirs, animals that the virus can live in without causing symptoms or disease. Those animal reservoirs can then pass the virus along to other animals and even people, causing illness. According to the World Health Organization (WHO), a common animal reservoir for multiple coronaviruses, including SARS-CoV and MERS-CoV, are bats. Bats can then infect other animals, which can go on to infect humans and make them sick.
Severe acute respiratory syndrome coronavirus (SARS-CoV)
SARS-CoV originated in southern China in November 2002. It caused a worldwide outbreak between 2002 and 2003, resulting in 8,098 probable cases and 774 deaths (9.6% mortality). There haven't been any SARS cases since 2004.
SARS-CoV was transmitted from horseshoe bats to civet cats, a small, lean nocturnal mammal. Infected civets were being sold for meat at local markets in southern China, which is how humans became infected with SARS-CoV.
SARS-CoV is readily spread person-to-person through close contact via respiratory droplets produced when someone who is sick sneezes or coughs. SARS-CoV can also survive in urine and feces for more than 2 days at room temperature, according to the World Health Organization (WHO). Most person-to-person transmission occurred in health care settings when adequate infection control measures were not followed.
Middle East respiratory syndrome coronavirus (MERS-CoV)
MERS-CoV originated in Saudi Arabia in 2012 and caused an outbreak localized to countries around the Arabian Peninsula. MERS infections are still occurring, with new cases being confirmed by the WHO as recently as January 13, 2020. Between 2012 and January 15, 2020, the WHO has reported 2,506 cases and 862 deaths (34.4% mortality).
MERS-CoV spread to humans from dromedary camels (also called Arabian camels, those with one hump on their back), which can carry the virus without getting sick. People who come in contact with camels that carry MERS-CoV, eat not fully cooked infected camel meat, drink unpasteurized infected camel milk, or drink infected camel urine (which is considered a medicine for various illnesses in the Middle East) can get sick with MERS.
There is limited evidence of person-to-person MERS-CoV transmission, with most such transmission happening after close contact with severely ill people in health care or household settings.
2019 novel coronavirus (SARS-CoV-2) and COVID-19
SARS-CoV-2, the newest human coronavirus, is currently causing a global pandemic of COVID-19. The virus is believed to have originated from Wuhan, China, though this is not a settled matter, and COVID-19 was first reported in December 2019.
Most of the people originally infected were sellers at the Huanan Seafood Wholesale Market in Wuhan, China, who sold live or recently killed fish, animals, and birds. The seafood market was quickly closed for cleaning and disinfection. Officials have yet to determine the animal that people got sick from.
SARS-CoV-2 is readily transmitted from person-to-person via respiratory droplets expressed when someone who is sick coughs, sneezes, talks, sings, and so on.
Like other respiratory illnesses, most coronaviruses are transmitted via respiratory droplets when someone coughs or sneezes.
In late March and early April 2020, mounting research highlighted that a "significant portion" of people with COVID-19 lack symptoms. These people may unknowingly spread the disease due to their lack of symptoms (asymptomatically) or may spread the disease before they develop symptoms (pre-symptomatically). This prompted the CDC to recommend that the general public wear cloth face coverings in public where social distancing is difficult to maintain, such as grocery stores and pharmacies.
The basic reproduction number (also called Ro, pronounced R-naught) of a virus is how many people, on average, one sick person usually infects. The higher the number, the more infectious a virus is. In general, a number greater than 1 typically means an epidemic will increase. While the basic reproductive number is constantly changing number based on the latest information, the WHO estimates a preliminary Ro of 2.0–2.5 for COVID-19. This means that up to 2.5 people can be infected by every 1 person infected with COVID-19. For comparison, the transmission rate of SARS-CoV was estimated to be 2-3 and that of common influenza strains is around 1.3.
To prevent coronavirus infection, you should follow the same preventive measures you do for other respiratory viruses like the common cold and flu, such as:
- Washing your hands regularly and thoroughly with soap and water for 20 seconds
- Using an alcohol-based hand sanitizer when you cannot wash your hands (or in addition to hand washing)
- Avoiding touching your eyes, nose, and mouth
- Cleaning and disinfecting objects regularly
- Avoiding close contact with people who are sick
- Staying home if you are sick
- Getting your flu shot
Due to the active community transmission of SARS-CoV-2 in the U.S. (and other countries around the world), the following precautions should also be followed to prevent the spread of SARS-CoV-2 and COVID-19.
If you are healthy and in an area of active transmission:
- Practice social distancing by minimizing contact with others and staying at least 6 feet away from others
- Avoid crowds and public places—stay home as much as possible (work and complete schoolwork at home)
- Avoid discretionary travel, shopping, and social visits
- Avoid eating in restaurants and bars—use the drive-thru, pickup or delivery instead
- Avoid visiting nursing homes, retirement facilities, and long-term care facilities
- Wear a cloth face mask (but be sure to properly use it by washing your hands before applying, keeping the mask over your mouth and nose while in public, never touching the front of the mask, and washing the mask after every use)
If you are in the following high-risk groups:
- If you are an older person or a person with underlying health conditions (such as diabetes, heart disease, asthma, a weakened immune system, etc.), stay home and avoid other people.
- If you or anyone in your household are sick or has tested positive for COVID-19, keep the entire household at home and call your medical provider—do not go to work or school.
There are currently no licensed human coronavirus vaccines. A SARS-CoV vaccine was created after the 2002 outbreak, but never used due to the outbreak being controlled before the vaccine was fully developed. Vaccines are currently being developed against both MERS-CoV and SARS-CoV-2.
Symptoms of a common coronavirus are similar to a cold or upper respiratory infection, such as:
- Stuffy nose
- Runny nose
- Sore throat
- General malaise (feeling unwell)
The more severe SARS-CoV, MERS-CoV, and SARS-CoV-2 strains can cause more severe symptoms and lower respiratory tract infections, such as pneumonia or bronchitis. More severe infections are more common in older people, infants, people with weakened immune systems, and people with underlying conditions such as heart disease.
SARS symptoms include:
- Fever and chills
- Body aches
- Other pneumonia symptoms (mucus-producing cough, shortness of breath, chest pain while coughing, nausea, vomiting, weakness)
MERS symptoms include:
- Fever and chills
- Shortness of breath
- Other pneumonia symptoms (mucus-producing cough, chest pain while coughing, nausea, vomiting, diarrhea, weakness)
COVID-19 symptoms. According to the CDC, people may have COVID-19 if they experience cough and shortness of breath or difficulty breathing, or if they have at least two of these symptoms:
- Fever and chills
- Repeated shaking with chills
- Muscle pain
- Sore throat
- New loss of taste or smell
Laboratory tests on blood or respiratory specimens (sputum or bronchoalveolar lavage) can detect the presence of a coronavirus by looking for its genetic sequence. Diagnostic kits for SARS-CoV-2 were made available by the CDC on February 4, 2020 to ship to qualified U.S. and international laboratories. As of March 30, the FDA has granted more than 20 diagnostic EUAs for SARS-CoV-2, including testing kits from LabCorp, Quest Diagnostics, Roche, Cepheid (rapid point-of care), and Abbott Laboratories (rapid point-of-care).
There are currently no approved coronavirus-specific antiviral treatments. The treatment for most coronaviruses is similar to how you would treat the common cold: rest, fluids, and over-the-counter medications for fever, sore throat, and congestion. More seriously ill patients may require hospitalization to receive medical care to help relieve their symptoms and ensure their organs are functioning properly, such as using a ventilator to assist with breathing.
There are currently no approved SARS-CoV-specific antivirals. There are also none in development because the outbreak was stopped by adequate infection control measures.
MERS-CoV-specific monoclonal antibodies created from a person who recovered from MERS are being pursued as antibody drugs.
A Phase 1 trial showed that a combination of two other monoclonal antibodies, called REGN3048 and REGN3051, were safe and well-tolerated in healthy adults.
Another Phase 1 clinical trial, conducted by the National Institute of Allergy and Infectious Disease (NIAID), showed that an experimental anti-MERS-CoV antibody, called SAB-301, was safe and well-tolerated in healthy adults. According to the NIAID, a Phase 2/3 trial is currently being planned for areas where MERS-CoV is still endemic, such as Saudi Arabia.
Currently available broad-spectrum antiviral drugs are being repurposed to see if they are effective against SARS-CoV-2. Corticosteroids, hydroxychloroquine (and the related chloroquine), Gilead's antiviral drug candidate remdesivir, and AbbVie's HIV drug Kaletra (lopinavir/ritonavir) are among the many drugs being studied in people with COVID-19. The first COVID-19 drug clinical trial began in the U.S. on February 25, 2020 studying Gilead's remdesivir in COVID-19 patients. In March 2020, WHO launched the global "Solidarity" clinical trial to test remdesivir, hydroxychloroquine and chloroquine, lopinavir/ritonavir, and lopinavir/ritonavir plus interferon beta-1a in COVID-19 patients worldwide.
On June 15, the FDA revoked the emergency use authorization (EUA) to use hydroxychloroquine and chloroquine to treat COVID-19. The agency reported that "these medicines showed no benefit for decreasing the likelihood of death or speeding recovery." On July 4, WHO discontinued its trials of hydroxychloroquine and lopinavir/ritonavirfor the same reasons.
Companies such as Sanofi, Regeneron, Lilly in collaboration with AbCellera, Ascletis, Takeda, and Vir Biotechnology are working on creating COVID-19-specific drugs.
Clinical trials treating COVID-19 patients with convalescent plasma (blood plasma taken from COVID-19 patients who have recovered) and hyperimmune globulin (a standardized, more concentrated version of convalescent plasma) began in the U.S. late March 2020.
A SARS-CoV vaccine was developed after the 2002 SARS outbreak. However, it was never used because the outbreak was under control and the virus' spread was halted before the vaccine was ready. It took about 20 months from when the SARS-CoV genome data was available until the vaccine was ready for human trials.
In July 2019, results from a Phase 1 clinical study showed that Inovio Pharmaceuticals and GeneOne Life Scienceâ€™s DNA vaccine candidate, called GLS-5300, was safe and well-tolerated in healthy adult volunteers. More than 85% of the 75 participants showed a detectable immune response to MERS-CoV comparable to MERS survivors after two doses of the vaccine candidate.
Another Phase 1 clinical trial started in December 2019 in Saudi Arabia studying the safety of another vaccine candidate, called chimpanzee adenovirus Oxford 1 (ChAdOx1), in healthy adults. The vaccine is made from a chimpanzee virus that cannot replicate and expresses a MERS protein.
The National Institute of Allergy and Infectious Disease (NIAID) and Moderna are collaborating to develop an mRNA vaccine. In January 2020, the company hoped to have a COVID-19 vaccine ready for human trials within three months, record-breaking speed if achieved. Moderna launched a Phase 1 clinical trial for their COVID-19 vaccine in March 2020, ahead of an already breakneck paced schedule.
The Coalition for Epidemic Preparedness Innovations (CEPI) is partially funding the NIAID and Moderna collaboration and two other vaccine development projects through the University of Queensland in Australia and with Inovio Pharmaceuticals. Inovio launched a Phase 1 clinical trial of their COVID-19 vaccine in early April 2020. That trial was the third COVID-19 vaccine trial to be launched, after Moderna and the China-based company CanSinoBio launched their Phase 1 vaccine trials in mid-March 2020.
NIAID is also collaborating with Oxford University to develop an adenovirus-vectored vaccine against COVID-19. Other companies who have jumped into the COVID-19 vaccine development race include Johnson & Johnson, Sanofi, GlaxoSmithKline (GSK), Pfizer in collaboration with BioNTech, Vaccitech, Hoth Therapeutics, and Arcturus Therapeutics.