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.

COVID-19 self-checker

Assess your symptoms on CDC’s coronavirus self-checker tool and find out if you’re a candidate for a COVID-19 test.

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.

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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 (within about 6 feet, or 2 meters). 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 twice or more, but this is uncommon.

The COVID-19 virus has mutated several times and now has several variants that are being monitored in the United States. The delta (B.1.617.2) variant is a variant of concern in the U.S. and is more contagious than previous variants.

Risk factors

Risk factors for COVID-19 appear to include:

  • Close contact (within 6 feet, or 2 meters) with someone who has COVID-19
  • Being coughed or sneezed on by an infected person

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 16 and older. The FDA has given emergency use authorization to Pfizer-BioNTech COVID-19 vaccines for ages 5 through 15.

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.

Also, if you are fully vaccinated, you can more safely return to many activities you may not have been able to do because of the pandemic. If you are in an area with a high number of new COVID-19 cases in the last week, the CDC recommends wearing a mask indoors in public and outdoors in crowded areas or when you are in close contact with unvaccinated people. If you are fully vaccinated and have a condition or are taking medications that weaken your immune system, you may need to keep wearing a mask.

An additional dose of a COVID-19 vaccine is recommended for people who are fully vaccinated and might not have had a strong enough immune response. In contrast, a booster dose is recommended for some people who are fully vaccinated and whose immune response weakened over time.

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

  • Additional dose. The CDC recommends a third dose 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. An additional dose might improve their protection against COVID-19.

    The third dose should be given at least 28 days after a second dose of an mRNA COVID-19 vaccine. The additional dose should be the same brand as the other two mRNA COVID-19 vaccine doses you 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. If you are age 18 or older, have been given both doses of the Pfizer-BioNTech COVID-19 vaccine or the Moderna COVID-19 vaccine and it’s been at least 6 months, you can get a single booster dose.

    If you are age 18 or older, have been given one dose of the Janssen/Johnson & Johnson COVID-19 vaccine and it’s been at least 2 months, you can get a single booster dose.

    Pregnant women may also receive a booster dose.

    You may choose which vaccine you get as a booster dose. You can get a booster dose that is the same brand as your previous shot or shots or choose a different brand.

If you haven’t had the COVID-19 vaccine, you can take many steps 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:

  • Avoid close contact (within about 6 feet, or 2 meters) with anyone who is sick or has symptoms.
  • Keep distance between yourself and others (within about 6 feet, or 2 meters). 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 and outdoors where there is a high risk of COVID-19 transmission, such as at a crowded event or large gathering. Further mask guidance differs depending on whether you are fully vaccinated or unvaccinated. Surgical masks may be used if available. N95 respirators should be reserved for health care providers.
  • 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, daily.
  • 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. Be prepared to wear a mask and 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.

Nov. 23, 2021
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