Overview

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 have also issued recommendations for preventing and treating the virus that causes COVID-19.

Symptoms

Signs and 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 (presymptomatic transmission). Common signs and symptoms can include:

  • Fever
  • Cough
  • Tiredness

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

Other symptoms can 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 (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.

People who are older have a higher risk of serious illness from COVID-19, and the risk increases with age. People who have existing medical conditions also may have a higher risk of serious illness. Certain medical conditions that may increase the risk of serious illness from COVID-19 include:

  • Serious heart diseases, such as heart failure, coronary artery disease or cardiomyopathy
  • Cancer
  • Chronic obstructive pulmonary disease (COPD)
  • Type 1 or type 2 diabetes
  • Overweight, obesity or severe obesity
  • High blood pressure
  • Smoking
  • Chronic kidney disease
  • Sickle cell disease or thalassemia
  • Weakened immune system from solid organ transplants or bone marrow transplants
  • Pregnancy
  • Asthma
  • Chronic lung diseases such as cystic fibrosis or pulmonary hypertension
  • Liver disease
  • Dementia
  • Down syndrome
  • Weakened immune system from bone marrow transplant, HIV or some medications
  • Brain and nervous system conditions, such as strokes
  • Substance use disorders

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

When to see a doctor

If you have COVID-19 signs or symptoms or you've been in contact with someone diagnosed with COVID-19, contact your health care provider right away for medical advice. Your health care provider will likely recommend that you get tested for COVID-19. If you have emergency COVID-19 symptoms, such as trouble breathing, seek care immediately. If you need to go to a hospital, call ahead so that health care providers can take steps to ensure that others aren't exposed.

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

  • Trouble breathing
  • Persistent chest pain or pressure
  • Inability to stay 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 provider 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.

Causes

Infection with severe acute respiratory syndrome coronavirus 2, or 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 can also 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 can also 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.

When a virus has one or more new mutations it’s called a variant of the original virus. The omicron (B.1.1.529) variant spreads more easily than the original virus that causes COVID-19 and the delta variant. However, omicron appears to cause less severe disease. People who are fully vaccinated can get breakthrough infections and spread the virus to others. But the COVID-19 vaccines are effective at preventing severe illness. This variant also reduces the effectiveness of some monoclonal antibody treatments. Omicron has a few major offshoots (sublineages), including BA.5 and BA.2.12.1. BA.5 made up about 88% of COVID-19 infections that had genetic sequencing in the U.S. in August, 2022, according to the CDC.

In April, the CDC downgraded the delta variant from a variant of concern to a variant being monitored. This means that the delta variant isn’t currently considered a major public health threat in the U.S.

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 air flow

Complications

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 (acute respiratory distress syndrome)
  • Blood clots
  • Acute kidney injury
  • Additional viral and bacterial infections

Prevention

The U.S. Food and Drug Administration (FDA) has given emergency use authorization to some COVID-19 vaccines in the United States. The FDA has approved the Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, to prevent COVID-19 in people age 12 and older. The FDA has given emergency use authorization to Pfizer-BioNTech COVID-19 vaccines for ages 6 months through 11.

The FDA has approved the Moderna vaccine, now called Spikevax, to prevent COVID-19 in people age 18 and older. The FDA has also authorized the Moderna COVID-19 vaccine in children ages 6 months through 17 years old. The FDA has also authorized the Novavax COVID-19, adjuvanted vaccine to prevent COVID-19 in people age 12 and older.

Due to the risk of a potentially life-threatening blood-clotting problem, the FDA is restricting use of the Janssen/Johnson & Johnson vaccine to certain people age 18 and older. Examples include people who had a severe allergic reaction after getting an mRNA COVID-19 vaccine and people who can't get an mRNA COVID-19 vaccine due to limited access or personal or religious concerns. If you get this vaccine, be sure to understand the risks and symptoms of the blood-clotting problem.

A vaccine can prevent you from getting the COVID-19 virus or prevent you from becoming seriously ill if you get the COVID-19 virus. In addition, COVID-19 vaccination might offer better protection than getting sick with COVID-19. A recent study showed that unvaccinated people who already had COVID-19 are more than twice as likely as fully vaccinated people to get reinfected with COVID-19.

After getting vaccinated, you can more safely return to many activities you may not have been able to do because of the pandemic. However, if you are in an area with a high number of people with COVID-19 in the hospital and new COVID-19 cases, the CDC recommends wearing a mask indoors in public. You're considered fully vaccinated two weeks after you get a second dose of an mRNA COVID-19 vaccine, after two doses of the Novavax vaccine, or two weeks after you get a single dose of the Janssen/Johnson & Johnson COVID-19 vaccine. You are considered up to date with your vaccines if you have gotten all recommended COVID-19 vaccines, including booster doses, when you become eligible.

An additional primary dose of a COVID-19 vaccine is recommended for people who are vaccinated and might not have had a strong enough immune response.

In contrast, a booster dose is recommended for people who are vaccinated and whose immune response weakened over time. Research suggests that getting a booster dose can decrease your risk of infection and severe illness with COVID-19.

People who have a moderately or severely weakened immune system should get an additional primary shot and a booster shot.

The CDC recommends additional doses and booster doses of COVID-19 vaccines in specific instances:

  • Additional primary shot. The CDC recommends an additional primary shot of an mRNA COVID-19 vaccine for some people with weakened immune systems, such as those who have had an organ transplant. People with weakened immune systems might not develop enough immunity after vaccination with two doses of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. An additional shot using an mRNA COVID-19 vaccine might improve their protection against COVID-19. This recommendation for an additional mRNA COVID-19 shot is for people ages 6 months and older.

    The additional primary shot should be given at least four weeks after a second dose of an mRNA COVID-19 vaccine or one dose of the Janssen/Johnson & Johnson COVID-19 vaccine. The additional primary shot should be the same brand as the other two mRNA COVID-19 vaccine doses that were given. If the brand given isn't known, either brand of mRNA COVID-19 vaccine can be given as a third dose.

  • Booster dose. These recommendations differ by age, what vaccines you have been given and the state of your immune system.

    Kids ages 5 through 11 can get a Pfizer-BioNTech COVID-19 booster based on the original viral strain, called a monovalent booster, if they have been given both doses of the Pfizer-BioNTech COVID-19 vaccine. They can get the booster if it’s been at least five months since the last shot.

    People ages 12 to 17 who had all recommended doses of the Moderna, Pfizer-BioNTech, or Novavax COVID-19 vaccines can only get the Pfizer-BioNTech COVID-19 updated, or bivalent, booster. This booster is based on the original virus strain and two Omicron strains. People can get this shot at least two months after their last shot.

    People who are ages 18 and older who had one of these COVID-19 vaccines may get either the Moderna or Pfizer-BioNTech COVID-19 bivalent booster at least two months after their last shot.

    If you are age 18 or older, and got the Janssen/Johnson & Johnson COVID-19 vaccine, you can get either of the mRNA vaccine bivalent boosters at least two months after your shot.

    Pregnant women may also receive a COVID-19 booster dose.

  • Booster doses for people with weakened immune systems. Kids ages 5 through 11 who have a weakened immune system should get a monovalent Pfizer-BioNTech COVID-19 vaccine booster shot if they have been given both all recommended doses of the Pfizer-BioNTech COVID-19 vaccine and it’s been at least three months since the additional primary shot.

    People age 12 to 17 who have a weakened immune system and have had all recommended doses of the Moderna, Pfizer-BioNTech or Novavax COVID-19 vaccines can get an updated, or bivalent, booster dose of the Pfizer-BioNTech COVID-19 vaccine. The bivalent booster can be given at least two months after the last shot.

    People age 18 and older who have a weakened immune system and have had all recommended doses of the COVID-19 vaccines can get a bivalent booster dose of either of the mRNA COVID-19 bivalent boosters. The bivalent booster can be given at least two months after the last shot.

The FDA has also authorized the monoclonal antibodies tixagevimab and cilgavimab (Evusheld) to prevent COVID-19 in some people with weakened immune systems or a history of severe reactions to a COVID-19 vaccine.

There are many steps you can take to reduce your risk of infection from the COVID-19 virus and reduce 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 air flow (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 and new COVID-19 cases, whether or not you're vaccinated. The CDC recommends wearing the most protective mask possible that you'll wear regularly, fits well and is comfortable.
  • Improve the air flow 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 might also consider a portable air cleaner.
  • 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, such as 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 doctor about other ways to protect yourself.

Travel

If you're planning to travel, first check the CDC and WHO websites for updates and advice. The CDC recommends that you wear a mask on 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 may also want to talk with your health care provider if you have health conditions that make you more susceptible to respiratory infections and complications.