What is the new coronavirus?

The novel coronavirus, which emerged in China in late 2019, can cause a serious respiratory disease known as COVID-19. While a majority of people who contract the virus will have mild illness or even no symptoms, some will develop severe lung disease, which may progress to pneumonia and respiratory failure that requires a mechanical ventilator. The coronavirus can also cause other complications, including heart problems, stroke and kidney failure.

How is the coronavirus transmitted?

The coronavirus (officially known as SARS-CoV-2) mainly spreads through respiratory droplets released when a person with the virus coughs, sneezes, talks or even breathes. The virus is mainly transmitted through the air, but it can also be spread when it lands on surfaces and someone touches these surfaces and then transfers it to their mouth, nose or eyes. A growing body of evidence shows that transmission appears to be uncommon outdoors and most common in crowded indoor spaces.

The coronavirus is detectable in the stool, but fecal spread is thought to be uncommon. Some studies have found the virus in semen, but it is not thought to be sexually transmitted. It is not yet known whether the coronavirus can be transmitted from mother to child during pregnancy or delivery.

How can transmission be prevented?

Several precautions can reduce transmission of the new coronavirus. People can transmit the virus even if they do not have symptoms, so it is important for everyone to observe such precautions even if they do not feel ill. 

  • Avoid close contact with other people, meaning within six feet.
  • Wash your hands with soap and water frequently and thoroughly.
  • Use hand sanitizer containing at least 60% alcohol if soap and water are not available.
  • Avoid touching your face, especially your mouth, nose and eyes.
  • Clean and disinfect surfaces that are frequently touched, such as doorknobs.
  • Stay home if you are sick.
  • Cough or sneeze into a tissue or your elbow.
  • Wear a cloth face mask when you are out in public (but save medical masks and respirators for health care workers).
  • Get vaccinated against the flu and pneumonia.

 More stringent prevention measures may be implemented in areas where the virus is spreading. These include social or physical distancing, such as avoiding close contact with people outside your household, staying away from public gatherings, working from home and closing schools. Some areas have implemented stay-at-home or shelter-in-place orders and closure of nonessential businesses.

Quarantine is a stricter approach that requires people who might have been exposed to the virus to stay at home or in a designated facility for a certain period of time. Isolation practices, including the use of personal protective equipment, are used when caring for a person with COVID-19 in the hospital.

Who is at risk for COVID-19?

While anyone can catch the new coronavirus, certain groups are at greater risk of developing more severe illness: 

  • People age 60 or older
  • People with compromised immune systems
  • People with preexisting health conditions, including cardiovascular disease, chronic lung disease, high blood pressure (hypertension), diabetes or obesity.

While older people and those with other health conditions are more likely to develop severe disease, young and healthy people can also become seriously ill. Although children seldom develop severe disease, they can carry the virus and transmit it to others. A small proportion of children develop a severe multisystem inflammatory syndrome.

People with HIV who are on effective antiretroviral treatment and have a high CD4 cell count do not appear to be more likely to contract the coronavirus or develop severe COVID-19. However, those who have unsuppressed HIV, currently have a low CD4 count or had a very low CD4 count in the past may be at greater risk.

People with cancer who are being treated with chemotherapy and those who have undergone bone marrow transplants often have low white blood cell counts and weakened immune systems and are prone to infections. Some studies have found that people living with cancer are more likely to develop severe disease.

What are the symptoms of COVID-19?

Around 80% of people with COVID-19 have mild or moderate illness and will recover without special treatment. About 15% will develop severe respiratory problems, and about 5% of cases are critical or life-threatening.

Some people who contract the coronavirus have few or no symptoms but can still transmit the virus to others. Some studies suggest that up to half of people who contract the virus may be asymptomatic.

The most common early symptoms of COVID-19 are cough, shortness of breath, fever, chills, muscle pain, sore throat and loss of the sense of taste or smell. A range of other symptoms have been reported, including headache, “pink eye” (conjunctivitis) and gastrointestinal symptoms such as nausea, vomiting or diarrhea. It takes around five days, on average, between exposure to the virus and the appearance of symptoms.

As the disease progresses, people may find it increasingly difficult to breathe. In serious cases, they may develop pneumonia, in which air sacs in the lungs (alveoli) fill with fluid, preventing oxygen from entering the bloodstream. In the most severe cases, patients can develop acute respiratory distress syndrome, or widespread lung inflammation that requires mechanical ventilation. Both the virus itself and the immune system’s response to it contribute to lung damage. Some people with severe COVID-19 experience an immune overreaction known as a cytokine storm than can lead to organ failure.

The COVID-19 mortality rate is not yet known because it remains uncertain how many people have contracted the virus. Many experts expect that the overall mortality rate will be around 1%, or about 10 times higher than that of a typical seasonal flu.

How is the coronavirus diagnosed?

SARS-CoV-2 can be diagnosed using a PCR RNA test that detects viral genetic material in a deep nasal swab sample. Saliva tests are also available. Viral antigen tests that detect fragments of viral proteins are simpler to perform but less accurate. Testing positive indicates current active infection. These tests are still in limited supply in many areas and they may be reserved for people with symptoms or suspected exposure.

Another type of test (known as a serology test) detects antibodies to the coronavirus in the blood, which reveal whether someone was infected in the past. Most experts expect that these antibodies will offer some protection against future infection, but it is not yet known how long this immunity might last.

If you think you may have been exposed to the coronavirus, contact a health care provider if you develop a fever, cough, difficulty breathing or other symptoms. Before you go to a clinic or hospital, call ahead so the staff can give you instructions and take appropriate precautions.

Does COVID-19 lead to immunity?

A year into the new pandemic, there’s still much to learn about immunity to SARS-CoV-2, the new coronavirus that causes COVID-19. After natural infection or vaccination, the immune system produces antibodies against the virus; this usually happens within a couple of weeks. People with compromised immunity–such as cancer patients, HIV-positive people who are not on treatment, and transplant recipients—may have a weaker response. Antibody levels in the blood decline over time, but the long-lived memory B cells that make antibodies remain on guard, ready to resume antibody production if they encounter the virus again. T cells, a different type of immune cell, also play a role in maintaining long-lasting protection. 

People who recover from COVID-19 appear to be protected for at least six months and likely much longer. Although antibody levels fall after a few months, memory B cell and T cell responses continue to provide protection. Vaccines appear to provide SARS-CoV-2 immunity similar to that of natural infection. But further follow-up is needed to see how long this protection lasts. So far, reinfection appears to be rare, with only a small number of confirmed cases reported. Most experts expect that population or herd immunity will be achieved when approximately 75% of the population has been exposed, either via natural infection or vaccination.

Click here for more information about COVID-19 immunity.


Is there a coronavirus vaccine?

COVID-19 vaccine development has occurred at an unprecedented pace. The first vaccines were authorized for emergency use in the United States in December 2020—less than a year after the genetic sequence of the SARS-CoV-2 coronavirus was discovered.

Three COVID-19 vaccines have received emergency use authorization from the Food and Drug Administration. All of these vaccines are highly effective at reducing the risk of severe illness. No one who received any of these vaccines in clinical trials was hospitalized or died from COVID-19. All of the vaccines are safe and generally well tolerated. Some recipients experience mild to moderate side effects including injection site reactions, fatigue and headache. Flu-like symptoms are not unusual after receiving vaccines and are an indication that the immune system is working. Severe allergic reactions (anaphylaxis) are rare and can be managed with medical care.

COVID-19 vaccines are in short supply, but production and distribution are ramping up rapidly in the United Stated. Health care workers and residents of long-term care facilities, people over 65, those with underlying health conditions that put them at risk for severe COVID-19 and certain frontline essential workers have been prioritized for vaccination. States and local jurisdictions make the final decisions about vaccine allocation.

Click here for more information about COVID-19 vaccines on our sister site COVIDHealth.com.


How is COVID-19 treated?

People with mild or moderate illness can usually manage their symptoms with supportive care at home, similar to care for the flu. This may include taking over-the-counter medications for fever, cough and pain, drinking plenty of fluids, using a humidifier and getting adequate rest.

In more severe cases, a person with COVID-19 may require hospitalization for more advanced care. This may involve breathing supplemental oxygen or, if patients can’t breathe on their own, the use of a ventilator machine.

There is one approved antiviral medication for COVID-19, remdesivir (Veklury), which is modestly effective for hospitalized patients. Several other drugs have shown activity against SARS-CoV-2 or related coronaviruses in laboratory and animal studies, and many clinical trials are underway.

Two monoclonal antibody regimens, bamlanivimab plus etesevimab and casirivimab plus imdevimab, have received emergency use authorization. Another treatment is convalescent plasma, which contains natural antibodies from people who have recovered from COVID-19.

Because most people recover without treatment, it is important to compare new therapies against an inactive placebo or different medications to see which ones work best. Be cautious about rumors and overly optimistic information about treatments that have not yet been tested in randomized clinical trials.

The Infectious Diseases Society of America has produced Guidelines on the Treatment and Management of Patients withCOVID-19. The recommendations are updated frequently to reflect new research.


For more information about COVID-19, the disease caused by the new coronavirus, please visit our sister site COVID Health.

Last Reviewed: March 3, 2021