Coronaviruses are a family of viruses that can cause illnesses such as the common cold, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS). In 2019, a new coronavirus was identified as the cause of a disease outbreak that originated in China.

The virus is known as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The disease it causes is called coronavirus disease 2019 (COVID-19).

In March 2020, the World Health Organization (WHO) declared the COVID-19 outbreak a pandemic.

Public health groups, including the U.S. Centers for Disease Control and Prevention (CDC) and WHO, are monitoring the COVID-19 pandemic and posting updates on their websites. These groups also have issued recommendations for preventing and treating the virus that causes COVID-19.


Symptoms of coronavirus disease 2019 (COVID-19) may appear 2 to 14 days after exposure. This time after exposure and before having symptoms is called the incubation period. You can still spread COVID-19 before you have symptoms. This is called presymptomatic transmission. Common symptoms can include:

  • Fever.
  • Cough.
  • Tiredness.

Early symptoms of COVID-19 may include a loss of taste or smell.

Other symptoms may include:

  • Shortness of breath or difficulty breathing.
  • Muscle aches.
  • Chills.
  • Sore throat.
  • Runny nose.
  • Headache.
  • Chest pain.
  • Pink eye (conjunctivitis).
  • Nausea.
  • Vomiting.
  • Diarrhea.
  • Rash.

This list isn't complete. Children have similar symptoms to adults and generally have mild illness.

The severity of COVID-19 symptoms can range from very mild to severe. Some people may have only a few symptoms. Some people may have no symptoms at all, but can still spread it. This is called asymptomatic transmission.

Some people may experience worsened symptoms, such as worsened shortness of breath and pneumonia, about a week after symptoms start. Some people experience COVID-19 symptoms for more than four weeks after they're diagnosed. These health issues are sometimes called post-COVID-19 conditions.

Some children experience multisystem inflammatory syndrome, a syndrome that can affect some organs and tissues, several weeks after having COVID-19. Rarely, some adults experience the syndrome too.

When to see a doctor

If you have COVID-19 symptoms or you've been in contact with someone diagnosed with COVID-19, contact your health care team right away for medical advice.

Your health care professional will likely recommend that you get tested for COVID-19.

If you have emergency COVID-19 symptoms, seek care immediately. Emergency symptoms can include:

  • Trouble breathing.
  • Constant chest pain or pressure.
  • Trouble staying awake.
  • New confusion.
  • Pale, gray or blue-colored skin, lips or nail beds — depending on skin tone.

This list isn't complete. Let your health care team know if you are an older adult or have chronic medical conditions, such as heart disease or lung disease, as you may have a greater risk of becoming seriously ill with COVID-19.

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Infection with severe acute respiratory syndrome coronavirus 2, also called SARS-CoV-2, causes coronavirus disease 2019 (COVID-19).

The virus that causes COVID-19 spreads easily among people. Data has shown that the COVID-19 virus spreads mainly from person to person among those in close contact. The virus spreads by respiratory droplets released when someone with the virus coughs, sneezes, breathes, sings or talks. These droplets can be inhaled or land in the mouth, nose or eyes of a person nearby.

Sometimes the COVID-19 virus can spread when a person is exposed to very small droplets or aerosols that stay in the air for several minutes or hours — called airborne transmission.

The virus also can spread if you touch a surface with the virus on it and then touch your mouth, nose or eyes. But the risk is low.

The COVID-19 virus can spread from someone who is infected but has no symptoms. This is called asymptomatic transmission. The COVID-19 virus also can spread from someone who is infected but hasn't developed symptoms yet. This is called presymptomatic transmission.

It's possible to get COVID-19 more than once.

Risk factors

Risk factors for COVID-19 appear to include:

  • Close contact with someone who has COVID-19, especially someone with symptoms.
  • Being coughed or sneezed on by an infected person.
  • Being near an infected person when in an indoor space with poor airflow.

Risk factors for serious COVID-19 illness

Some people are at a higher risk of serious COVID-19 illness than others. This includes people who are older, and the risk increases with age.

People with existing medical conditions also may have a higher risk of serious illness. This includes people who have:

  • Sickle cell disease or thalassemia.
  • Serious heart diseases, such as heart failure, coronary artery disease or cardiomyopathy, and possibly high blood pressure.
  • Chronic kidney, liver or lung diseases.

People with dementia or Alzheimer's are also at higher risk, as are people with brain and nervous system conditions such as stroke. Smoking increases the risk of serious COVID-19 illness. And people with body mass index in the overweight category or obese category may have an increased risk as well.

Other medical conditions that may increase the risk of serious illness from COVID-19 include:

  • Cancer.
  • Type 1 or type 2 diabetes.
  • Weakened immune system from solid organ transplants or bone marrow transplants, some medicines, or HIV.
  • Pregnancy.
  • Down syndrome.
  • Substance use disorders.

This list is not complete. Other medical conditions may increase your risk of serious illness from COVID-19.


Although most people with COVID-19 have mild to moderate symptoms, the disease can cause severe medical complications and lead to death in some people.

Older adults or people with existing medical conditions are at greater risk of becoming seriously ill with COVID-19.

Complications can include:

  • Pneumonia and trouble breathing.
  • Organ failure in several organs.
  • Heart problems.
  • A severe lung condition that causes a low amount of oxygen to go through your bloodstream to your organs, called acute respiratory distress syndrome.
  • Blood clots.
  • Acute kidney injury.
  • Additional viral and bacterial infections.


The CDC recommends a COVID-19 vaccine for everyone age 6 months and older. The COVID-19 vaccine can lower the risk of death or serious illness caused by COVID-19. It lowers your risk and lowers the risk that you may spread it to people around you.

Getting a COVID-19 vaccine also is important because the flu and COVID-19 may be spreading at the same time and cause similar symptoms. Getting a COVID-19 vaccine and a flu vaccine is the best way to protect against both.

The FDA has approved or authorized these COVID-19 vaccines in the U.S.:

  • The Moderna and Pfizer-BioNTech COVID-19 vaccines. These vaccines protect against the original strain of the virus that causes COVID-19 and the omicron variant of the original virus strain. These are called bivalent vaccines.
  • The Novavax COVID-19 vaccine. This vaccine protects against the original strain of the virus that causes COVID-19.

The COVID-19 vaccination schedule in the U.S. depends on a person's age, immune system and previous vaccinations. In general, people age 6 months through 11 years can get either the Moderna or Pfizer-BioNTech COVID-19 vaccines. People age 12 and older can choose the Moderna, Pfizer-BioNTech or Novavax COVID-19 vaccines.

You are considered up to date on COVID-19 vaccines depending on age and vaccine type:

Kids age 6 months to age 5

  • Kids age 6 months up to age 4 are up to date if they had three doses of the Pfizer-BioNTech COVID-19 vaccine and at least one dose included the omicron variant.
  • At age 5, kids who got the Pfizer-BioNTech COVID-19 vaccine are caught up if they had at least one dose that included the omicron variant.
  • Kids age 6 months through age 5 who got the Moderna COVID-19 vaccine are up to date after two doses, as long as at least one included the omicron variant.

People age 6 and older

  • The CDC recommends that everyone age 6 and older should have one vaccine dose that includes the omicron strain. This vaccine needs to be in addition to any other COVID-19 vaccines received in the past.
  • People older than age 6 with typical immune systems are up to date with their COVID-19 vaccines after one shot with either the Pfizer-BioNTech or Moderna COVID-19 vaccines that include the original and omicron strains.
  • People age 12 and older who chose the Novavax vaccine are up to date after two shots. But the CDC recommends people get one shot of either the updated Pfizer-BioNTech or Moderna COVID-19 vaccines at least two months after the last Novavax shot.
  • If you originally got the Janssen/Johnson & Johnson shot, get an updated Moderna or Pfizer-BioNTech COVID-19 vaccine in order to get up to date with your COVID-19 vaccines.

People with weakened immune systems

Your health care team may suggest added doses of COVID-19 vaccine if you have a moderately or severely weakened immune system. The CDC suggests getting doses of the Moderna or Pfizer-BioNTech COVID-19 vaccines within the shortest time period for some people. This includes those with weakened immune systems, people age 65 and older, and others who need rapid protection.

Vaccination and other actions

You can take many steps to lower your risk of infection from the COVID-19 virus and lower the risk of spreading it to others. WHO and CDC recommend following these precautions:

  • Get vaccinated. COVID-19 vaccines reduce the risk of getting and spreading COVID-19.
  • Avoid close contact with anyone who is sick or has symptoms.
  • Keep distance between yourself and others when you're in indoor public spaces. This is especially important if you have a higher risk of serious illness. Keep in mind some people may have COVID-19 and spread it to others, even if they don't have symptoms or don't know they have COVID-19.
  • Avoid crowds and indoor places that have poor airflow, also called ventilation.
  • Wash your hands often with soap and water for at least 20 seconds. Or use an alcohol-based hand sanitizer that contains at least 60% alcohol.
  • Wear a face mask in indoor public spaces if you're in an area with a high number of people with COVID-19 in the hospital. The CDC recommends wearing the most protective mask possible that you'll wear regularly, fits well and is comfortable.
  • Improve the airflow indoors. Open windows. Turn on fans to direct air out of windows. If you can't open windows, consider using air filters. And turn on exhaust fans in your bathroom and kitchen. You also might consider using a portable air cleaner.
  • Cover your mouth and nose. Cover your mouth and nose with your elbow or a tissue when you cough or sneeze. Throw away the used tissue. Wash your hands right away.
  • Avoid touching your eyes, nose and mouth.
  • Avoid sharing dishes, glasses, towels, bedding and other household items if you're sick.
  • Clean and disinfect high-touch surfaces. For example, clean doorknobs, light switches, electronics and counters regularly.
  • Stay home from work, school and public areas, and stay home in isolation if you're sick, unless you're going to get medical care. Avoid public transportation, taxis and ride-hailing services if you're sick.

If you have a chronic medical condition and may have a higher risk of serious illness, check with your health care professional about other ways to protect yourself.


If you're planning to travel, first check the CDC and WHO websites for updates and advice.

The CDC suggests wearing masks in close quarters. This includes planes, buses, trains and other indoor public transportation traveling to, within or out of the U.S., as well as in places such as airports and train stations.

Use appropriate hand hygiene when in public.

You also may want to talk with your health care team if you have health conditions that make you more susceptible to respiratory infections and complications.

July 14, 2023
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