Coronavirus disease 2019 (COVID-19)

Overview

Coronavirus disease 2019 (COVID-19), is an illness caused by a virus. The virus is called severe acute respiratory syndrome coronavirus 2 or, more commonly, SARS-CoV-2. It started spreading at the end of 2019 and became a pandemic disease in 2020.

The virus that causes COVID-19 spreads between people in close contact. Most commonly, it spreads through the air in tiny droplets of fluid. Many people with COVID-19 have mild illness or no symptoms. But for older adults and people with certain medical conditions, COVID-19 can lead to the need for care in the hospital or death.

Staying up to date on your COVID-19 vaccine helps prevent serious illness, the need for hospital care due to COVID-19 and death from COVID-19. Other things that may help prevent the spread of this coronavirus include good indoor airflow, physical distancing, wearing a mask in the right setting and good hygiene.

Medicine can limit the seriousness of the viral infection. Most people recover without long-term effects, but some people have symptoms that continue for months.

Symptoms

Typical COVID-19 symptoms often show up 2 to 14 days after contact with the virus.

Symptoms can include:

• Dry cough.
• Shortness of breath.
• Loss of taste or smell.
• Extreme tiredness, called fatigue.
• Digestive symptoms such as upset stomach, vomiting or loose stools, also called diarrhea.
• Pain, such as headaches and body or muscle aches.
• Fever or chills.
• Coldlike symptoms such as congestion, runny nose or sore throat.

People may have only a few symptoms or none at all. People who have no symptoms but test positive for COVID-19 are called asymptomatic. For example, many children who test positive don't have symptoms of COVID-19 illness. People who go on to have symptoms are considered presymptomatic. People in both groups can still spread the COVID-19 virus to others.

Some people may have symptoms that get worse about 5 to 7 days after symptoms start.

Most people with COVID-19 have mild to moderate symptoms. But COVID-19 can cause serious medical complications and lead to death. Older adults and people who already have medical conditions are at greater risk of serious illness.

COVID-19 may be a mild, moderate, severe or critical illness.

• In broad terms, mild COVID-19 doesn't affect the ability of the lungs to get oxygen to the body.
• In moderate COVID-19 illness, the lungs work properly but there are signs that the infection is deep in the lungs.
• Severe COVID-19 means that the lungs don't work correctly, and the person needs oxygen and other medical help in the hospital.
• Critical COVID-19 illness means the lungs and breathing system, called the respiratory system, have failed and there is damage throughout the body.

Rarely, people who catch this coronavirus can develop a group of symptoms linked to inflamed organs or tissues. This illness is called multisystem inflammatory syndrome. When children have this illness, it is called multisystem inflammatory syndrome in children (MIS-C). In adults, the name is MIS-A.

When to see a doctor

People who are at high risk of serious illness may get medicine to block the spread of the COVID-19 virus in the body. Or your healthcare team may plan regular checks to monitor your health.

Get emergency help right away for any of these symptoms in adults:

• Trouble breathing or catching your breath.
• Skin, lips or nail beds that are pale, gray or blue.
• New confusion.
• Trouble staying awake or waking up.
• Chest pain or pressure that is constant.

Get emergency help right away for any of those symptoms in children, as well as the following symptoms:

• Dizziness.
• Dry mouth, crying with few or no tears, or less need to urinate, suggesting dehydration.
• Frequent vomiting or loose stools, called diarrhea, for longer than 24 hours.
• Fever that doesn't go away.
• Trouble staying awake or waking up.
• Being confused or agitated.

This list doesn't include every emergency symptom. If you or a person you're taking care of has symptoms that worry you, get help. Let the healthcare team know about a positive test for COVID-19 or symptoms of the illness.

Causes

COVID-19 is caused by infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

The coronavirus spreads mainly from person to person, even from someone who is infected but has no symptoms. When people with COVID-19 cough, sneeze, breathe, sing or talk, their breath may contain the COVID-19 virus.

The coronavirus carried by the breath of a person with the infection can land directly on the face of a nearby person, after a sneeze or cough, for example. The droplets or particles could also be breathed in by other people if they are close together or in areas with low airflow.

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

• Over time, the body's defense against the COVID-19 virus can fade.
• A person may be exposed to so much of the virus that it breaks through the immune defense.
• As a virus infects a group of people, the virus copies itself. During this process, the genetic code can randomly change in each copy. The changes are called mutations. If the coronavirus that causes COVID-19 changes in ways that make previous infections or vaccination less effective at preventing infection, people can get sick again.

The virus that causes COVID-19 can infect some pets. Cats, dogs, hamsters and ferrets have caught this coronavirus and had symptoms. It's rare for a person to get COVID-19 from a pet.

Risk factors

The main risk factors for COVID-19 are:

• Living with someone who has COVID-19.
• Spending time in places with poor airflow and a higher number of people when the virus is spreading.
• Spending more than 30 minutes in close contact with someone who has COVID-19.

Many factors affect your risk of catching the virus that causes COVID-19. How long you are in contact with the virus, whether the space has good airflow and the activities you're doing in the space all affect the risk. Also, your risk may change based on whether you or others wear masks, whether someone has COVID-19 symptoms, and how close you are to others. Close contact includes sitting next to and talking to other people, for example, or sharing a car or bedroom.

It seems to be rare for people to catch the COVID-19 virus from an infected surface. While the virus is shed in waste, called stool, COVID-19 infection from places such as public bathrooms is not common.

Serious COVID-19 illness risk factors

Some people are at a higher risk of serious COVID-19 illness than others are. This includes people age 65 and older as well as babies younger than 6 months. People in those age groups have the highest risk of needing hospital care for COVID-19.

Serious illness also is a higher risk for people who have weakened immune systems. This may be from a condition such as cancer or HIV. Or from medicines that people may take after organ transplant or during cancer treatment. The risk of serious COVID-19 illness also goes up if someone is pregnant.

Other conditions that raise the risk of serious COVID-19 illness are:

• Heart disease, high blood pressure and heart failure.
• Stroke.
• Diabetes.
• Chronic kidney, liver or lung disease.
• Mood disorders or mental health conditions, such as schizophrenia.
• Sickle cell disease.
• Smoking.
• Body mass index in the obese category.

This list is not complete. Factors linked to a health issue may raise the risk of serious COVID-19 illness too. Examples are living in a group home or lack of access to medical care.

Complications

Complications of severe COVID-19 illness can include:

• Acute respiratory distress syndrome, which is when the body's organs do not get enough oxygen.
• New heart issues or shock caused by the infection or heart conditions.
• Overreaction of the immune system, called the inflammatory response.
• Blood clots.
• Damage to brain function, called encephalopathy.
• Kidney injury.

COVID-19 illness also may worsen medical issues a person already manages.

Post-COVID-19 syndrome

After having COVID-19, some people report that their symptoms continue for months or they develop new symptoms. This syndrome has often been called long COVID. You might hear it called long-haul COVID-19, post-COVID conditions or post-acute sequelae of SARS-CoV-2 (PASC).

Other infections, such as the flu and polio, can lead to long-term illness. But the virus that causes COVID-19 has only been studied since it began to spread in 2019. So research into the specific effects of long-term COVID-19 symptoms continues.

Researchers do think that post-COVID-19 syndrome can happen after COVID-19 illness of any severity.

Getting a COVID-19 vaccine may help prevent post-COVID-19 syndrome.

Prevention

The 2025-2026 COVID-19 vaccines available in the United States include Moderna, Pfizer-BioNTech and Novavax. The vaccines are all approved for people age 65 and older. Each vaccine also is approved for younger people with a health condition that raises the risk of serious COVID-19 illness.

Moderna COVID-19 vaccine 2025-2026 formulas:

• Spikevax. This vaccine is approved for all people age 65 and older and for people ages 6 months to 64 years with a risk of serious COVID-19 illness.
• Mnexspike. This vaccine is approved for all people age 65 and older and for people ages 12 to 64 years with a risk of serious COVID-19 illness.

Pfizer-BioNTech COVID-19 vaccine 2025-2026 formula:

• Comirnaty. This vaccine is approved for all people age 65 and older and for people ages 5 to 64 years with a risk of serious COVID-19 illness.

Novavax COVID-19 vaccine 2025-2026 formula:

• Nuvaxovid. This vaccine is approved for all people age 65 and older and for people ages 12 to 64 years with a risk of serious COVID-19 illness.

Risks linked to serious COVID-19 illness

The risk of getting seriously ill with COVID-19 depends on a range of factors. Information gathered since 2019 shows that the risk of serious COVID-19 illness goes up depending on your age, your health, and where you live or work.

You are more likely to get seriously ill if you:

• Are over age 65.
• Are pregnant.
• Have a weakened immune system due to illness or medicine you take.
• Already have a chronic illness.
• Spend time in places with poor airflow and a higher number of people when the virus is spreading.
• Spend more than 30 minutes in close contact with someone who has COVID-19.

Smoking increases the risk of serious COVID-19 illness. And people with a body mass index in the obese category may have a higher risk as well.

This list is not complete. Not every risk factor for serious COVID-19 illness is known. People of all ages who have no other medical issues have needed hospital care for COVID-19.

Who should get a COVID-19 vaccine?

Getting a COVID-19 vaccine protects against serious illness, the need for hospital care due to COVID-19 and death from COVID-19. Staying up to date with the latest vaccine is most important for people at higher risk. That includes adults over age 65, those with weakened immune systems, people who are pregnant, and people with chronic conditions, such as heart disease, lung disease or obesity.

Serious side effects from the COVID-19 vaccine are extremely rare. Because of that, even healthy adults benefit from the COVID-19 vaccine, which lowers the risk of serious illness at a rate similar to that of the flu vaccine.

Most people are up to date after one dose of the 2025-2026 COVID-19 vaccine from any vaccine maker. Children ages 6 months to 23 months are up to date after two doses of Spikevax, spaced at least four weeks apart.

People with weakened immune systems

Your healthcare team may suggest added doses of COVID-19 vaccine if you have a moderately or seriously weakened immune system. In the U.S., the Food and Drug Administration (FDA) also has authorized the monoclonal antibody pemivibart (Pemgarda) to prevent COVID-19 in some people with weakened immune systems.

Control the spread of the virus

In addition to vaccination, there are other ways to stop the spread of the virus that causes COVID-19.

If you are at a higher risk of serious illness, talk with your healthcare professional about how best to protect yourself. Know what to do if you get sick so you can quickly start treatment.

If you feel ill or have COVID-19, stay home and away from others, including pets, if possible.

In general, make it a habit to:

• Test for COVID-19. If you have symptoms of COVID-19 test for the illness. Or test five days after coming in contact with the virus.
• Help from afar. Avoid close contact with anyone who is sick or has symptoms, if possible.
• Wash your hands. Wash your hands well and often with soap and water for at least 20 seconds. Or use an alcohol-based hand sanitizer with at least 60% alcohol.
• Cover your coughs and sneezes. Cough or sneeze into a tissue or your elbow. Then wash your hands.
• Clean and disinfect high-touch surfaces. For example, clean doorknobs, light switches, electronics and counters regularly.

Try to spread out in crowded public areas, especially in places with poor airflow. This is important if you have a higher risk of serious illness.

Wear a mask when you're inside a crowded place with poor airflow. This is most important when many people in the area are sick with COVID-19 or the flu.

Travel and COVID-19

Travel brings people together from areas where illnesses may be present at higher levels. Masks can help slow the spread of viruses that cause respiratory diseases in general, including COVID-19. Masks help the most in places with low airflow and places where you are in close contact with other people. Also, masks can help if the places you travel to or through have high levels of illness.

Masking is especially important if you or a companion have a high risk of serious COVID-19 illness.

Diagnosis

If you have symptoms of coronavirus disease 2019 (COVID-19) or you've been exposed to the COVID-19 virus, contact your healthcare team. Let them know whether you've had close contact with anyone diagnosed with COVID-19.

In the United States, at-home COVID-19 tests are available. The U.S. Food and Drug Administration (FDA) approves or authorizes the tests. On the FDA website, you can find a list of the tests that are validated and their expiration dates. You also can check with your healthcare professional before buying a test if you have any concerns.

When taking a test at home, carefully read the directions that come with the test. Follow the instructions exactly to get as accurate a result as possible.

Here are some guidelines for when to take a COVID-19 test:

• If you have COVID-19 symptoms, test for the illness right away.
• If you were exposed to the COVID-19 virus but don't have symptoms, wait at least five days after exposure and then test.
• If you have symptoms and tested positive for COVID-19 within the last 30 days, you can test again. But if you were recently exposed to the coronavirus and don't have symptoms, you don't need to test.

Also, testing before an event or contact with people at high risk of serious illness helps prevent the spread of the virus that causes COVID-19.

COVID-19 tests use a sample taken from your nose or throat, or a sample of saliva.

Two types of tests can help diagnose COVID-19.

• Molecular tests. These tests look for genetic material from the COVID-19 virus. Polymerase chain reaction (PCR) tests are molecular tests. You also may see this type of test referred to as a nucleic acid amplification test (NAAT). PCR tests are more accurate than the other type of COVID-19 test, called an antigen test. PCR tests may be done at home. But they are much more likely to be done by a healthcare professional and processed in a lab.
• Antigen tests. These tests look for viral proteins called antigens. Antigen tests also may be called rapid COVID-19 tests or at-home COVID-19 tests. These tests are useful if you need a quick result. Antigen tests are reliable and accurate, but they are less accurate than PCR tests. This is especially true if you don't have symptoms. If you take an antigen test and the result shows that you do not have COVID-19, called a negative result, take another antigen test after 48 hours to get the most accurate result.

Understanding test results

If you have a positive result with a COVID-19 PCR or antigen test, you almost certainly have COVID-19. Another test isn't needed.

If you get a negative PCR test result, you most likely do not have COVID-19.

If you have a negative antigen test result, the FDA recommends that you repeat an antigen test two days after the first test. Whether or not you have symptoms, repeating the test helps get the correct diagnosis.

If you test positive, call a healthcare professional immediately to find out what options are available.

Preventing the spread of the COVID-19 virus while sick

To prevent the spread of the COVID-19 virus to others, stay home and apart from anyone you live with for as long as you have worsening symptoms. If you have a weakened immune system, you will likely need to isolate for longer. How long depends on your symptoms and personal health history. Your healthcare professional can advise you on what's best in your situation.

If you must be around others, a face mask helps lower the spread of this coronavirus. During this time, try not to share items such as cups or towels. Use a separate bathroom and bedroom. Getting more airflow in your home can help as well.

Once you're feeling better and haven't had a fever for a full 24 hours, and you haven't taken medicine for fever during that time, you can go back to being around others. If your fever returns or you start to feel worse, return to isolation until your symptoms improve and you are fever-free without medicine for 24 hours. But listen to the advice of your healthcare professional.

In the five days after isolation, to help prevent the spread of the COVID-19 virus, you can wear a mask, wash your hands, keep your distance from others, take a COVID-19 test and improve airflow.

Treatment

Many people with COVID-19 recover with rest, plenty of fluids and care that manages symptoms. Medicine you can get without a prescription can help, such as:

• Fever reducers.
• Pain relievers, such as ibuprofen (Advil, Motrin IB, others) or acetaminophen (Tylenol, others).
• Cough syrup or medicine.

If you are at high risk of serious COVID-19 illness, your healthcare professional may suggest medicine to prevent mild illness from getting worse. These medicines can include nirmatrelvir-ritonavir (Paxlovid), remdesivir (Veklury) or molnupiravir (Lagevrio).

Nirmatrelvir-ritonavir and molnupiravir are taken by mouth as pills. Remdesivir is given through an IV.

If you're very ill, you may need to be treated in the hospital.

Treatment for serious COVID-19 illness

People who are in the hospital for COVID-19 treatment receive care based on their immune system response and the need for oxygen support.

Added oxygen may be given through a tube in the nose. Some people may need to have a tube placed in their airways to push air into the lungs. That's called mechanical ventilation. In very severe situations, a machine called extracorporeal membrane oxygenation (ECMO) can be used to mimic the function of the heart and lungs.

Medicines for severe COVID-19 may be remdesivir, baricitinib (Olumiant) or tocilizumab (Actemra), or a corticosteroid such as dexamethasone.

Baricitinib is a pill. Tocilizumab is given through an IV. Dexamethasone may be given either as a pill or through an IV.

Another treatment option may come from blood donated by people who have recovered from COVID-19. This treatment is called convalescent plasma. The blood is processed to remove blood cells, leaving behind a liquid called plasma that has immune system proteins called antibodies. Convalescent plasma with high antibody levels may be used to help people with weakened immune systems recover from COVID-19.

Lifestyle and home remedies

If you have COVID-19, it's important to get plenty of rest, drink fluids and watch your symptoms. Medicines you can get without a prescription can help manage pain, fever or cough.

If you have COVID-19 and are staying separate from others, try to keep busy and help your body clear out the infection. These steps might help:

• Eat healthy meals.
• Get enough sleep.
• Try relaxation exercises.
• Do activities you enjoy.
• Connect with friends and family, such as with phone or video calls.

People who have COVID-19 or care for someone with the illness may feel new or worse symptoms of stress, depression and anxiety. If you or someone you know needs help with managing the stress of illness, isolation or caregiving, contact your healthcare professional. Consider asking for a referral to a mental health professional.

Preparing for an appointment

To be treated for COVID-19, you may start by seeing your primary healthcare professional. Or you may be referred immediately to a specialist trained in treating infectious diseases.

Here's some information to help you get ready for your appointment.

What you can do

When you make the appointment, ask if there's anything you need to do in advance. Make a list of:

• Your symptoms, including any that don't seem related to the reason for your appointment.
• Your recent travel, including any international travel.
• Key personal information, including major stresses, recent life changes and family medical history.
• All medicines, vitamins and other supplements you take, including the doses.
• Questions to ask your healthcare team.

Take a family member or friend along, if possible, to help you remember the information you're given.

Some basic questions to ask your healthcare team include:

• How likely is it that COVID-19 is causing my symptoms?
• What are other possible causes for my symptoms?
• What tests do I need?
• What course of action do you recommend?
• Are there restrictions I need to follow?
• Should I see a specialist?

What to expect from your doctor

Your healthcare professional is likely to ask you several questions, such as:

• When did your symptoms begin?
• Where have you traveled recently?
• Who have you been in close contact with?
• How bad are your symptoms?