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 now known as the 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 pandemic and posting updates on their websites. These groups have also issued recommendations for preventing and treating the illness.

Symptoms

Signs and symptoms of coronavirus disease 2019 (COVID-19) may appear two to 14 days after exposure. This time after exposure and before having symptoms is called the incubation period. 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 is not all inclusive. 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, and some people may have no symptoms at all. Some people may experience worsened symptoms, such as worsened shortness of breath and pneumonia, about a week after symptoms start.

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
  • Pregnancy
  • Asthma
  • Chronic lung diseases such as cystic fibrosis or pulmonary fibrosis
  • Liver disease
  • Dementia
  • Down syndrome
  • Weakened immune system from bone marrow transplant, HIV or some medications
  • Brain and nervous system conditions
  • Substance use disorders

This list is not all inclusive. Other underlying 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 doctor or clinic right away for medical advice. Tell your health care team about your symptoms and possible exposure before you go to your appointment.

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 all inclusive. Let your doctor 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. During the pandemic, it's important to make sure health care is available for those in greatest need.

Causes

Infection with the new coronavirus (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, and more continues to be discovered over time about how it spreads. Data has shown that it 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.

In some situations, the COVID-19 virus can spread by a person being exposed to small droplets or aerosols that stay in the air for several minutes or hours — called airborne transmission. It's not yet known how common it is for the virus to spread this way.

It can also spread if a person touches a surface or object with the virus on it and then touches his or her mouth, nose or eyes, but the risk is low.

Some reinfections of the virus that causes COVID-19 have happened, but these have been uncommon.

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 U.S. The FDA has approved the Pfizer-BioNTech COVID-19 vaccine, now called Comirnaty, to prevent COVID-19 in people age 16 and older. 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. Also, if you are fully vaccinated, you can return to many activities you may not have been able to do because of the pandemic — including not wearing a mask or social distancing — except where required by a rule or law. However, 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.

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 the COVID-19 virus.

An additional dose of an mRNA COVID-19 vaccine is aimed at helping people who might not have had a strong enough immune response after their previous doses. In contrast, a booster dose would be given to people whose immune response weakened over time.

Currently, the CDC and the FDA state that people in the U.S. who have been fully vaccinated don’t need a vaccine booster. This is because fully vaccinated people are protected from severe disease and death with the COVID-19 virus, including from COVID-19 variants. Most COVID-19 hospitalizations and deaths are among people who are unvaccinated.

If you haven’t had the COVID-19 vaccine, you can take many steps to reduce your risk of infection. WHO and CDC recommend following these precautions for avoiding exposure to the virus that causes COVID-19:

  • 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 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 if you're sick, unless you're going to get medical care. Avoid public transportation, taxis and ride-sharing 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 doctor if you have health conditions that make you more susceptible to respiratory infections and complications.