Merck Manual

Please confirm that you are not located inside the Russian Federation

Quick Facts



The Manual's Editorial Staff

Last full review/revision May 2020| Content last modified May 2020
Click here for the Professional Version
Get the full details
NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version

What is COVID-19?

COVID-19 is a potentially severe viral infection that affects your lungs and airways.

  • It's caused by a new type of coronavirus

  • The virus spreads very easily to other people

  • COVID-19 is now everywhere in the world

  • Some infected people have no symptoms, but others get very sick, and some people die

  • Doctors test swabs from your nose or throat to diagnose COVID-19

  • No medicines cure COVID-19, but doctors are testing some that might help

  • Doctors are also working on a vaccine to prevent COVID-19

What is a pandemic?

COVID-19 is a pandemic. That's an infection that's spreading rapidly in many parts of the world all at once.

What causes COVID-19?

COVID-19 is caused by a new type of coronavirus called SARS-CoV-2. Doctors call it new because it hasn't been around before. It recently changed (mutated) from a type of coronavirus that infects bats.

The virus spreads:

  • Through the air, in droplets that an infected person spreads through a cough or sneeze

  • Through touching things that infected people have touched and then touching your face

Unlike with many respiratory viruses, you can spread the virus that causes COVID-19 before you have any symptoms. If you don't know you have the virus, you can easily pass it on and not know it.

Also COVID-19 spreads from person to person much easier than other respiratory infections like colds or the flu.

What is a coronavirus?

There are hundreds of different coronaviruses that are all related. Most of them infect only animals.

  • Only a few coronaviruses can infect people

  • Some of them cause only colds

  • Three coronaviruses cause very serious illness and can be fatal

Besides COVID-19, the other serious coronavirus infections are called SARS and MERS. Hardly anyone gets those infections anymore.

What are the symptoms of COVID-19?

Many people with COVID-19, particularly children, have almost no symptoms.

If you do get symptoms, you'll likely have:

  • Fever

  • Dry cough

  • Trouble breathing

  • Feeling really weak and tired

You may also have:

  • Runny nose and sore throat

  • Loss of your sense of smell and taste

  • Headaches

  • Stomach problems such as nausea and diarrhea

A bad infection gets deep in your lungs, causing viral pneumonia. That will make you very short of breath. A bad infection can also affect a lot of organs, including your brain, heart, and kidneys.

Is COVID-19 fatal?

You can die from COVID-19. The older you are, the higher your risk of death. Most deaths occur in people over 50 years old. People over 80 are at very high risk. But even children and young adults can die.

You're also at higher risk if you:

  • Have other medical problems such as heart disease, high blood pressure, or diabetes

  • Are a man

  • Are black

How can doctors tell if I have COVID-19?

The most common test uses:

  • A swab taken from the back of your nose or throat

The swab is sent to a lab to look for the virus.

A blood test can look for antibodies your immune system has made to defend against the virus. It takes your body a few weeks to make these antibodies, so this test is not useful when you first get sick. But it can help tell whether you were ever infected.

If you're short of breath, doctors will usually:

  • Do a chest x-ray to look for pneumonia

  • Measure the oxygen level in your blood with a fingertip sensor

How is COVID-19 treated?

If you have a mild or moderate case, you'll:

  • Stay home and not go out or go near other people (isolation)

  • Wear a mask so you don't spread the virus

  • Take acetaminophen or ibuprofen for fever and aches

If you have a severe case, with breathing problems, you'll need to go to the hospital. Doctors will:

  • Give you oxygen

  • Sometimes put you on a ventilator

You may need to be on a ventilator for up to a few weeks.

There are no medicines that are proven to kill the virus, but doctors are trying some that might help.

If you have problems with your kidneys, you may need dialysis.

How can I prevent COVID-19?

The best way to prevent COVID-19 is to avoid being exposed to the virus. These actions help:

  • Stay about 6 feet (2 meters) away from people in public (social distancing)

  • Wear a cloth face mask when you're in public (see Use of Cloth Face Coverings to Help Slow the Spread of COVID-19)

  • Wash your hands often with soap and water for at least 20 seconds

  • Use an alcohol-based hand sanitizer

  • Avoid touching your eyes, nose, and mouth with unwashed hands

  • Cover a cough or sneeze with a tissue, then throw the tissue in the trash

  • Use a household disinfectant spray or wipe to clean things people touch a lot, like door handles, phones, remote controls, and countertops

Is there a vaccine for COVID-19?

There's no vaccine yet, though many doctors are working to develop one. Experts think a vaccine will be available some time in 2021.

Drugs Mentioned In This Article

Generic Name Select Brand Names
NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Also of Interest

3D Models
View All
3D Model