Symptoms of COVID-19 vary significantly.
Two types of tests can be used to diagnose a COVID-19 infection.
Measures should be taken to prevent infection, particularly vaccination, social distancing, and masking.
Treatment of COVID-19 depends on how severe the illness is and the likelihood that the person will develop severe disease.
COVID-19 was first reported in late 2019 in Wuhan, China and has since spread extensively worldwide. For current information on the number of cases and deaths, see the Centers for Disease Control and Prevention: 2019 Novel Coronavirus and the World Health Organization Coronavirus (COVID-19) Dashboard.
The coronavirus that causes COVID-19 is called SARS-CoV-2. It is related to but slightly different from the coronavirus that causes SARS Severe Acute Respiratory Syndrome (SARS) Coronaviruses are a large family of viruses that cause respiratory illness ranging in severity from the common cold to fatal pneumonia. There are many different coronaviruses. Most of them cause... read more .
Transmission of COVID-19
COVID-19 is mainly spread from person to person through respiratory droplets that are produced when an infected person coughs, sneezes, sings, exercises, or talks. The virus spreads through both large respiratory droplets that can travel short distances and through small respiratory particle aerosols that can linger in the air for several hours and travel longer distances (> 6 feet) before being inhaled. In general, the closer and longer the interaction with an infected person, the higher the risk of the virus spreading. Factors such as distance from an infected person, duration of time in the presence of an infected person, the size of the air space, and the direction and speed of airflow can contribute to this risk. People may also get a COVID-19 infection by touching something that has the virus on it and then touching their own mouth, nose, or eyes.
The virus is usually transmitted by a person with symptoms of the infection. However, the virus can be transmitted by people before they exhibit symptoms (presymptomatic) and even by people who are infected but never develop symptoms (asymptomatic).
Situations with high risk of transmission include congregate living facilities (for example, nursing homes, long-term care facilities, residential schools, prisons, ships) and crowded, poorly ventilated environments (such as indoor religious services, gyms, bars, night clubs, indoor restaurants, and meat-packing facilities). The residents of nursing homes are also at high risk of severe disease because of age and underlying medical disorders.
The recent Delta and Omicron variants of the SARS-CoV-2 virus are more readily transmitted than the earlier variants (see CDC: Delta Variant: What We Know About the Science). On November 30, 2021, the United States designated Omicron as a "variant of concern." The Centers for Disease Control and Prevention (CDC) has been collaborating with global public health partners to learn about Omicron. (See also CDC: Omicron Variant: What You Need to Know.)
Symptoms of COVID-19
Symptoms vary in people with COVID-19. Most people infected with COVID-19 have mild symptoms or no symptoms at all, but some become severely ill and die. Symptoms can include the following:
Congestion or runny nose
Shortness of breath or difficulty breathing
Chills or repeated shaking with chills
New loss of smell or taste
Nausea or vomiting
If people develop symptoms, they usually appear about 2 to 14 days after being infected. For the Omicron variant, symptoms usually appear in only 2 to 4 days.
The risk of serious disease and death in people with COVID-19 increases with age, in people who smoke, and in people with other serious medical disorders, such as cancer, heart, lung, kidney, or liver disease, sickle cell disease, diabetes, obesity, or immunocompromising disorders. For all age groups, risk of serious disease and death decreases in people who are vaccinated against COVID-19 Vaccination COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more .
In addition to respiratory disease that can be severe and lead to death, other serious complications include
Heart disorders including arrhythmias Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more , heart muscle disorders, and acute heart injury
Coagulation disorders Overview of Blood Clotting Disorders Blood clotting (coagulation) disorders are dysfunctions in the body's ability to control the formation of blood clots. These dysfunctions may result in Too little clotting, leading to abnormal... read more including blood clots in small and large blood vessels as well as bleeding
A rare complication called multisystem inflammatory syndrome in children (MIS-C) that may be linked to COVID-19 has been reported in children. Symptoms of this can be similar to the rare condition Kawasaki disease Kawasaki Disease Kawasaki disease causes inflammation of blood vessels throughout the body. The cause of Kawasaki disease is unknown but may be associated with an infection. Children typically have fever, rash... read more and include fever, abdominal pain, and rash. Vaccination helps protect against developing MIS-C. A similar complication has been reported in young and middle-aged adults (multisystem inflammatory syndrome in adults [MIS-A]).
In most people, symptoms resolve over about a week. However, in a few people, symptoms last longer, most often with shortness of breath, cough, and extreme fatigue, sometimes persisting for weeks. In 25 to 50% of people with COVID-19, symptoms last for months. This has been referred to by many names, including long COVID, long-haul COVID, and post-acute COVID-19 syndrome or condition.
Although infection with coronaviruses is generally believed to provide some degree of immunity to reinfection, the duration and effectiveness of immunity following COVID-19 remain unknown. Symptoms associated with reinfection tend to be similar to or milder than the initial infection.
Diagnosis of COVID-19
Tests to identify the virus
Doctors suspect COVID-19 in people who have symptoms of the infection. Recent close contact with someone who has COVID-19 increases the likelihood of infection. People who suspect they may have COVID-19 should call their doctor before being tested and before arriving at a clinic so appropriate precautions can be taken.
The following people should be tested for COVID-19 (also see CDC: Overview of Testing for SARS-CoV-2):
People who have been in close contact with a COVID-19–infected person—get tested about 5 days after last contact and, if not up-to-date on COVID-19 vaccinations, quarantine Quarantine and isolation COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more
People who are not up-to-date on COVID-19 vaccinations who are prioritized for expanded community screening for COVID-19
People asked to test because of school, workplace, health care setting, or government requirements
People who took part in activities that put them at higher risk for COVID-19, such as attending large social gatherings or being in crowded indoor settings without correct and consistent masking, may also want to be tested.
There are two types of tests to diagnose COVID-19 infection:
NAAT (nucleic acid amplification test)
There are multiple types of NAATs. RT-PCR (real-time reverse transcriptase–polymerase chain reaction) tests, often simply called PCR tests, are the type of NAAT that have the highest sensitivity and specificity, meaning they are more accurate and thus the preferred initial test for COVID-19. RT-PCR tests can be done on upper and lower respiratory secretions (samples from nasal or oral swabs or saliva) to identify the virus.
Antigen tests can be done at home or in a health care setting, but they are generally less accurate than NAATs, including RT-PCR tests. Therefore, it may be necessary to confirm some antigen test results (for example, a negative test in a person with symptoms) with a RT-PCR or other NAAT. Many antigen test kits also recommend repeating the test over several days to increase the likelihood of detecting infection. Also, some tests may not detect the Omicron variant (see FDA: SARS-CoV-2 Viral Mutations: Impact on COVID-19 Tests).
Another type of test is called an antibody test. Antibody tests (also called serologic tests) are not used for diagnosing current infections. Antibody tests help determine whether the person being tested was previously infected, which is important for tracking cases and studying the virus.
Prevention of COVID-19
The best way to prevent infection is be fully vaccinated Vaccination COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more . In addition to being vaccinated, people should avoid being exposed to the virus by taking steps recommended by the CDC.
Masking and other routine measures
The Centers for Disease Control and Prevention (CDC) provides the following guidance regarding wearing a well-fitting face mask, covering both mouth and nose (see CDC: Use Masks to Slow the Spread of COVID-19):
Everyone 2 years or older who is not fully vaccinated should wear a mask in indoor public places.
Everyone, regardless of vaccination status, should wear a mask when in indoor public places in areas with high numbers of COVID-19 cases.
In areas with high numbers of COVID-19 cases, everyone 2 years or older regardless of vaccination status should wear a mask in crowded outdoor settings and for outdoor activities with close contact with others who are not fully vaccinated.
People who have a condition or are taking medications that weaken their immune system may not be fully protected even if they are fully vaccinated. They should continue to take all precautions recommended for unvaccinated people, including wearing a well-fitted mask when around others, until advised otherwise by their health care practitioner.
Everyone should wear a mask when sick and around other people.
Everyone should wear a mask when caring for someone who is sick.
Different types of masks provide different levels of protection, including (in increasing order of protection): multi-layer cloth masks; multi-layer surgical masks; KF94, KN95, or K95 masks. People may also be required to wear a mask by local laws, regulations, or rules or business or workplace guidance, and this may vary by vaccination status (see CDC: Types of Masks and Respirators).
In addition to wearing a mask, people who are not fully vaccinated should practice "social distancing" (keeping 6 feet between people who do not live in the same household).
In addition, the CDC recommends the following routine actions to help prevent the spread of respiratory viruses:
Washing hands often with soap and water for at least 20 seconds, especially after going to the bathroom, before eating, and after blowing the nose, coughing, or sneezing
Using an alcohol-based hand sanitizer with at least 60% alcohol if soap and water are not readily available
Avoiding touching eyes, nose, and mouth with unwashed hands
Avoiding close contact with people who are sick
Staying home when sick
Covering cough or sneeze with a tissue, then throwing the tissue in the trash
Cleaning and disinfecting frequently touched objects and surfaces using a regular household cleaning spray or wipe
Monitoring health for potential symptoms and taking temperature if symptoms develop
Quarantine and isolation
To help prevent the spread of COVID-19, the Centers for Disease Control and Prevention (CDC) recommends quarantine and isolation measures. (See also CDC: Quarantine and Isolation.)
Quarantine is meant to separate people who had "close contact" with a contagious person so they do not infect other people.
Close contact is having been within 6 feet of a person with COVID-19 for a total of 15 minutes or more during a 24-hour period. An infected person can start spreading the infection 2 days before symptoms start or before testing positive for COVID-19.
For students in kindergarten through 12th grade in an indoor or outdoor class setting where masks were worn correctly and consistently, close contact is defined as having been within 3 feet of an infected person (see CDC: Close Contact).
Quarantine begins on the day of the close contact, which is considered Day 0 (counting days of quarantine starts on Day 1). People who are not up-to-date on COVID-19 vaccinations should quarantine through Day 5 and wear a well-fitting mask through Day 10. If quarantine is not possible, the person should wear a well-fitting mask at all times when around others through Day 10.
The following people who had close contact with an infected person do not need to quarantine but should wear a well-fitting mask through Day 10:
People who are up-to-date on COVID-19 vaccinations
People who had COVID-19 infection (confirmed by a positive test) within 90 days prior to exposure
Exposed people should have a COVID-19 test 5 to 7 days after having a close contact, regardless of whether they have symptoms or are vaccinated. If the exposed person has symptoms that could be from COVID-19, that person should immediately isolate until getting a negative COVID-19 test.
Isolation separates people with confirmed or suspected COVID-19 from those without COVID-19. The CDC recommends isolation for people with COVID-19 symptoms and/or who have a positive COVID-19 test. People who are in isolation should stay home and separated from others, or wear a well-fitting mask when they need to be around others in the home.
Isolation should begin the day symptoms start or the day a person tests positive for COVID-19, which is considered Day 0 (counting days of isolation starts on Day 1) and lasts at least through Day 5.
People may stop isolating on Day 6 as long as the person has been fever-free for at least 24 hours, without the use of fever-reducing drugs, and the symptoms are getting better. They should wear a well-fitting mask through Day 10 when around others.
If a person has access to a COVID-19 test, the test may be done on or after Day 5 of the isolation period. If the test result is positive, isolation should continue through Day 10. If the test result is negative, isolation may end, but a well-fitting mask should be worn around others at home and all other places through Day 10.
People who were severely ill should isolate through Day 10 at least.
Vaccination remains the most effective strategy at preventing severe illness and death from COVID-19 with the recent and currently circulating variants, Delta and Omicron. Hospitalization rates in the United States in the fall of 2021 were 8 to 10 times higher in unvaccinated people than vaccinated people. Unvaccinated people were also 20 times more likely to die from COVID-19 than vaccinated people in that timeframe.
Following the recommendations for vaccination is very important for people's own health and for the health of their family and the people in their community. Multiple COVID-19 vaccines are currently in use worldwide (see COVID-19 Vaccine Tracker). In the United States, for people who are not immunocompromised, vaccines are administered on the following schedule (see CDC: Key Things to Know About COVID-19 Vaccines):
Primary series: 1 injection OR 2 injections either 3 or 4 weeks apart, depending on the vaccine
Booster dose: Additional injection at least 2 to 5 months after the primary series, depending on the vaccine
Two mRNA vaccines have received full approval and one adenovirus vector vaccine has received Emergency Use Authorization (EUA) from the US Food and Drug Administration (FDA).
BNT162b2, the COVID-19 vaccine (mRNA) with the brand name Comirnaty produced by Pfizer-BioNTech, is FDA-approved for people age 16 years and older. It is available under Emergency Use Authorization for use in people 5 to 15 years of age. The primary series for this vaccine is 2 injections, 3 weeks apart. (See also FDA: Fact Sheet for Healthcare Providers [Pfizer-BioNTech].)
mRNA-1273, the COVID-19 vaccine (mRNA) produced by Moderna, is FDA-approved for people age 18 years and older. The primary series for this vaccine is 2 injections, 4 weeks apart. (See also FDA: Fact sheet for Healthcare Providers [Moderna].)
Adenovirus vector vaccine
Ad26.COV2.S, the COVID-19 vaccine (adenovirus vector) produced by Janssen/Johnson & Johnson, is available under Emergency Use Authorization for use in people age 18 years and older. Primary vaccination is a single injection. (See also FDA: Fact sheet for Healthcare Providers [Janssen].)
In most situations, the mRNA vaccines (from Pfizer-BioNTech and Moderna) are preferred over the vector vaccine (from Janssen/Johnson & Johnson) for primary series and booster doses due to the slight risk of serious side effects with the vector vaccine (see CDC: Johnson & Johnson’s Janssen COVID-19 Vaccine Overview and Safety.)
An additional primary dose is advised for people with moderately to severely compromised immune systems . People should talk to their health care practitioner about their medical condition and whether getting an additional primary dose is appropriate for them (see also CDC: Guidance for COVID-19 vaccination for people who are moderately or severely immunocompromised). The following guidance has been released:
Moderately to severely immunocompromised people age 18 years and older who completed their mRNA-1273 vaccine primary series (from Moderna) should plan to get an additional primary dose at least 28 days after receiving their second shot and a booster shot Vaccination COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more at least 3 months later.
Moderately to severely immunocompromised people age 5 years and older who completed their BNT162b2 vaccine primary series (from Pfizer-BioNTech) should plan to get an additional primary dose at least 28 days after receiving their second shot. Those who are 12 years and older should also get a booster shot Vaccination COVID-19 is an acute respiratory illness that can be severe and is caused by the coronavirus named SARS-CoV-2. Symptoms of COVID-19 vary significantly. Two types of tests can be used to diagnose... read more at least 3 months later.
Moderately to severely immunocompromised people age 18 years and older who received the Ad26.COV2.S vaccine (from Janssen/Johnson & Johnson) should get a second shot (additional dose) using an mRNA COVID-19 vaccine at least 28 days after receiving their Ad26.COV2.S shot and a booster shot at least 2 months later. (People who received a first shot of the Ad26.COV2.S vaccine and already received a booster dose without having had the second mRNA primary shot should get an mRNA shot as a third dose at least 2 months after the booster dose.)
Protection against infection from a primary vaccination series has been shown to decrease over time. To maximize protection against infection, severe disease, and death, booster doses are recommended 2 to 5 months after the primary series is completed. People who have received a booster dose when eligible are considered "up-to-date" on their vaccine series.
People age 12 years and older are eligible for a booster shot. (See also CDC: COVID-19 Vaccine Booster Shots.)
Booster doses are recommended for all BNT162b2 vaccine recipients who are age 12 years and older and completed their primary series at least 5 months ago (3 months ago, if immunocompromised).
Booster doses are recommended for all mRNA-1273 vaccine recipients who are age 18 years and older and completed their initial 2-dose series (or their third primary dose, if immunocompromised) at least 5 months ago (3 months ago, if immunocompromised).
Booster doses are recommended for Ad26.COV2.S vaccine recipients who are age 18 years and older and who received their first dose of the vaccine at least 2 months ago. (Immunocompromised people who received a second shot using an mRNA COVID-19 vaccine after receiving their Ad26.COV2.S shot should get a booster dose at least 2 months after their second shot.)
Eligible people may choose to receive a booster dose of any available COVID-19 vaccine (BNT162b2, mRNA-1273, or Ad26.COV2.S), regardless of which vaccine they initially received. In most situations, the mRNA vaccines (from Pfizer-BioNTech and Moderna) are preferred over the vector vaccine (from Janssen/Johnson & Johnson) due to the slight risk of serious side effects with the vector vaccine. (Unlike people age 18 years and older who can choose any available COVID-19 vaccine as a booster shot, only a BNT162b2 booster shot produced by Pfizer-BioNTech is currently approved for people age 12 to 17 years.)
For additional details and information about side effects, see COVID-19 Vaccine COVID-19 Vaccine Coronavirus disease 2019 (COVID-19) vaccines provide protection against COVID-19. COVID-19 is the disease caused by infection with the SARS-CoV-2 virus. There are multiple COVID-19 vaccines... read more .
Treatment of COVID-19
Drugs to relieve fever and muscle aches
Sometimes, remdesivir and/or dexamethasone
Sometimes, antiviral drugs for mild to moderate infection
Sometimes, monoclonal antibodies
Treatment of COVID-19 depends on how severe the illness is and the likelihood that the person will develop severe disease.
For mild illness, resting at home is often sufficient. Acetaminophen or a nonsteroidal anti-inflammatory drug (NSAID), such as ibuprofen, may be taken to relieve fever and muscle aches. Despite initial anecdotal concerns, there is no scientific evidence that the use of NSAIDs worsens COVID-19. Similarly, there is no scientific evidence that people with COVID-19 who take the blood pressure drugs called angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARBs) should stop taking them.
For more severe illness, some people require hospitalization with treatment that might include supplemental oxygen or mechanical ventilation Mechanical Ventilation Mechanical ventilation is use of a machine to aid the movement of air into and out of the lungs. Some people with respiratory failure need a mechanical ventilator (a machine that helps air get... read more .
For people with severe illness from COVID-19 or people at high risk for progression to severe disease, some drug and other therapies are recommended. This is a rapidly evolving topic (see National Institutes of Health (NIH) COVID-19 Treatment Guidelines and Infectious Diseases Society of America (IDSA) Guidelines on the Treatment and Management of Patients with COVID-19).
Remdesivir (an antiviral drug) is for the treatment for select people hospitalized with COVID-19. Remdesivir is given intravenously. The recommended treatment duration is 5 days. The combination of remdesivir and the corticosteroid dexamethasone is commonly used in hospitalized people who need supplemental oxygen.
The combination drug nirmatrelvir and ritonavir is an antiviral drug taken by mouth. It may be used to treat mild to moderate COVID-19 infection in some adults and adolescents who are at high risk for progression to severe COVID-19, including hospitalization or death. It is not authorized for use for longer than 5 consecutive days.
Molnupiravir is an antiviral drug taken by mouth. It may be used to treat mild to moderate COVID-19 infection in nonhospitalized adults who are at high risk for progression to severe COVID-19, including hospitalization or death, and for whom alternative COVID-19 treatment options are not available or appropriate. Molnupiravir is taken by mouth and is not authorized for use for longer than 5 consecutive days. It is not recommended for use during pregnancy.
Three monoclonal antibodies may be used to treat mild to moderate COVID-19 in adults and pediatric patients (12 years or older and weighing at least 88 pounds) with COVID-19 and who are at high risk for progressing to severe disease (includes those who are 65 years or older or who have certain chronic medical conditions). Only one of the three is effective against the Omicron variant. Monoclonal antibodies are given intravenously or by a single-dose injection.
The following therapies are NOT recommended for the treatment or prevention of COVID-19:
Blood plasma from recovered patients
Nonspecific immunoglobulin (IVIG) and mesenchymal stem cell therapy
Additional immunomodulatory therapies, including interferons, kinase inhibitors, and interleukin inhibitors
Azithromycin and antiretrovirals
Lopinavir/ritonavir (an HIV retroviral)
Chloroquine and hydroxychloroquine (antimalaria drugs)
Ivermectin (an antiparasite drug): the FDA and other organizations have issued warnings about toxicity from the inappropriate use of ivermectin preparations intended for large animal use (see FDA: Why You Should Not Use Ivermectin to Treat or Prevent COVID-19).
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.