What Is COVID-19? Symptoms, Causes, Diagnosis, Treatment, and Prevention

COVID-19 is an infectious disease caused by a new (or novel) coronavirus, SARS-CoV-2, that was first discovered in 2019. It has since caused more than 770 million confirmed cases globally, leading to 7 million deaths, according to the World Health Organization (WHO).

There currently is no cure for COVID-19, but there are approved and investigational treatments. International groups of scientists have also created COVID-19 vaccines, with three extremely effective ones available in the United States.

On top of the powerful protection of vaccines, people can take other precautions to avoid getting and spreading COVID-19.

Common Questions & Answers

What are the common symptoms of COVID-19?
Common symptoms of COVID-19 include sore throat, runny or blocked nose, sneezing, cough (with or without phlegm), headache, hoarse voice, muscle aches, or altered sense of smell. Other symptoms include fever or chills, fatigue, and gastrointestinal issues.
Who is at higher risk for severe COVID-19?
Older adults, especially those over 65, are at higher risk for severe COVID-19. Additionally, individuals with chronic diseases such as cancer, diabetes, heart conditions, obesity, and weakened immune systems are also at higher risk.
How is COVID-19 diagnosed?
COVID-19 can be diagnosed through three types of tests: molecular tests (PCR tests), antigen tests, and antibody tests. Molecular tests are the most accurate and are used to determine if someone is currently infected. Antigen tests provide rapid results but are less accurate. Antibody tests detect past infection and recovery.
What are the available treatments for COVID-19?
There are several treatments for COVID-19, including antiviral therapies like nirmatrelvir with ritonavir (Paxlovid), remdesivir (Veklury), and molnupiravir (Lagevrio). Immunocompromised individuals may benefit from convalescent plasma. Over-the-counter medications like acetaminophen or ibuprofen can help relieve symptoms in mild or moderate cases.
How can COVID-19 be prevented?
COVID-19 can be prevented through various measures, including vaccination, avoiding close contact with infected individuals, wearing masks in high-risk areas, practicing good hand hygiene, maintaining physical distance in crowded spaces, improving indoor ventilation, and regularly cleaning high-touch surfaces.

Signs and Symptoms of COVID-19

Many people with COVID-19 experience symptoms ranging from mild to life-threatening. Symptoms may appear 2 to 14 days after coronavirus exposure, according to the Centers for Disease Control and Prevention (CDC), although a significant number of people with COVID-19 are asymptomatic, meaning they never develop any symptoms.

According to the UK-based Zoe Health Study, the 10 most common symptoms of the COVID-19 caused by the omicron variant are:

  1. Sore throat
  2. Runny nose
  3. Blocked (stuffy) nose
  4. Sneezing
  5. A cough without phlegm
  6. Headache
  7. A cough with phlegm
  8. A hoarse voice
  9. Muscle aches and pains
  10. An altered sense of smell

Other symptoms of COVID-19, according to the CDC, include fever or chills, fatigue, and gastrointestinal issues such as nausea, vomiting, or diarrhea.

Signs of severe COVID-19 warrant emergency medical attention, says the CDC. These include:

  • Shortness of breath or difficulty breathing
  • Persistent pain or pressure in the chest
  • New confusion
  • Inability to wake or stay awake
  • Pale, gray, or blue-colored skin, lips, or nail beds

Causes and Risk Factors of COVID-19

COVID-19 mainly spreads through respiratory fluids (droplets and small particles called aerosols that float in the air) emitted from an infected person’s mouth or nose when they cough, sneeze, speak, sing, or breathe, according to the WHO.

Another person can become infected if they inhale the fluids or if the fluids come into contact with their eyes, nose, or mouth.

The WHO says the risk of COVID-19 transmission is highest in three settings:

  • Crowded places
  • Close-contact settings, especially where people have conversations very near each other
  • Confined and enclosed places with poor ventilation

Anyone with COVID-19 can spread it, even if they don’t have symptoms, says the CDC.

Age and COVID-19 Risk

Older people (especially those over age 50) who contract COVID-19 are at higher risk for a more severe case than younger people, with the risk increasing with age, says the CDC. Most COVID-19-related deaths occur in people older than 65.

Seniors who are unvaccinated or who have a disability, weakened immune system, or certain medical conditions are at especially high risk.

Health Conditions and COVID-19 Risk

A number of chronic diseases are known to increase the chances a person will develop severe illness from COVID-19. According to the CDC, the conditions that demonstrably increase risk in adults of any age include:

Children at increased risk of severe COVID-19 include those with complex medical problems; neurological, genetic, or metabolic conditions; and congenital heart disease. Children with conditions such as obesity, asthma, or chronic lung disease, diabetes, or sickle cell disease, or who are immunocompromised, are also particularly vulnerable to severe COVID-19, per the CDC.

Variants and COVID-19 Risk

All viruses, including the virus that causes COVID-19, constantly change by mutating, creating new variants and subvariants. In many cases these new forms of the virus quickly disappear or remain at very low levels, but sometimes they spread, displacing their viral competitors.

SARS-CoV-2 variants have evolved over time, from alpha, beta, and delta to omicron, the currently dominant variant, says Yale Medicine. Subvariants of omicron are considered especially contagious because of the high number of mutations on their spike protein, the part of the virus that attaches to human cells.

The three COVID-19 vaccines available in the United States significantly decrease the risk of serious illness and death caused by omicron and its subvariants. When so-called breakthrough infections occur in people who have been immunized, those illnesses are likely to be less severe than they would be in unvaccinated individuals, says the Infectious Diseases Society of America (IDSA).

How Is COVID-19 Diagnosed?

There are three types of tests for COVID-19: molecular tests (also called PCR tests), antigen tests, and antibody tests.

Molecular (PCR) Tests

Typically requiring a trip to a testing site, molecular tests are used to determine if someone is currently infected with COVID-19. A PCR (polymerase chain reaction) test looks for the virus’s genetic material. Specimens can be collected with a nasal or throat swab or through a saliva sample, says the FDA, then sent to a laboratory for analysis. Molecular tests are considered more accurate than other types of COVID-19 tests.

Antigen (Rapid or Home) Tests

Most home COVID-19 tests are antigen tests. Antigen tests look for specific proteins from the coronavirus. Although not as accurate as PCR tests, antigen tests don’t require as much equipment and results are usually delivered in minutes.

If you test negative, test again after 48 hours (whether or not you have symptoms) to reduce the odds you’ve received a so-called false-negative result, says the FDA.

Antibody Tests

These tests use a finger prick or blood draw to look for COVID-19 antibodies — an immune response to COVID-19. For anyone who hasn’t received a COVID-19 vaccine, the presence of antibodies indicates past infection and recovery, according to the FDA.

Duration of COVID-19

When it comes to how long a person might feel sick with COVID-19, there is a broad spectrum. “Some people never feel sick or have symptoms — that’s one extreme,” says David Lee Thomas, MD, MPH, an infectious-disease specialist and a professor of medicine at Johns Hopkins Medicine in Baltimore. “On the other side, you have individuals who were infected with the virus over three months ago and have not stopped feeling sick.”

While most people with COVID-19 get better within a couple of days or weeks, some people don’t recover fully, developing a condition called long COVID. The CDC defines long COVID as “a wide range of new, returning, or ongoing health problems that people experience after infection with the virus that causes COVID-19.”

Long COVID isn’t identifiable until at least four weeks after the initial coronavirus infection, per the CDC.

Treatment and Medication Options for COVID-19

People with mild or moderate COVID-19 who are not at high risk for severe COVID-19 can get relief from symptoms from over-the-counter medications like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin), per the CDC.

COVID-19 treatments for people at high risk of serious illness can help prevent an infection from developing into severe illness. All these antiviral therapies work best when taken as soon as possible after the onset of symptoms, says the CDC.

The treatments are:

  • Nirmatrelvir with ritonavir (Paxlovid) The FDA has approved this oral medication to treat mild or moderate COVID-19 in adults and children age 12 and up who are at high risk for progression to severe COVID-19. Treatment with Paxlovid must begin within five days of the onset of symptoms.
  • Remdesivir (Veklury) Both adults and children are eligible for this intravenous medication, administered over three consecutive days at a healthcare center. Treatment must begin within seven days of the onset of symptoms.
  • Molnupiravir (Lagevrio) This oral medication is for adults, who must begin taking it within five days of the onset of symptoms.

To find doctors, health centers, and pharmacies near you where Paxlovid or Lagevrio is available, use the COVID-19 Test to Treat Locator. Another program, Home Test to Treat, simplifies access to free COVID-19 tests and treatment for those who are eligible.

People who are immunocompromised may benefit from an experimental treatment called convalescent plasma, says the CDC.

Certain individuals who are hospitalized with severe COVID-19 may receive drugs such as remdesivir (Veklury); the rheumatoid arthritis drugs baricitinib (Olumiant) and tocilizumab (Actemra); and the steroid dexamethasone, says Mayo Clinic.

Prevention of COVID-19

Here’s a rundown of the different ways to stave off COVID-19.

COVID-19 Vaccines

There are currently three main brands of COVID-19 vaccines available in the United States, for use as primary vaccines and as boosters.

Pfizer-BioNTech and Moderna vaccines As the CDC explains, these vaccines build immunity against COVID-19 using a genetic molecule called messenger RNA (mRNA).

The mRNA in the vaccine contains instructions that help the body’s own cells produce a harmless piece of a protein resembling one that exists on the surface of the coronavirus; this triggers an immune response.

Novavax COVID-19 vaccine This vaccine uses a more traditional technology than mRNA vaccines. It is a “protein subunit” vaccine, meaning the vaccine contains parts of the coronavirus’s spike protein, stimulating an immune response, plus another ingredient called an adjuvant that strengthens protection.

Note that the Johnson & Johnson (J&J) COVID-19 vaccine is no longer administered in the United States as of May 2023.

The CDC recommends that everyone 6 months of age and older stay up-to-date on their COVID-19 vaccines. People who are immunocompromised should follow a special vaccination schedule, per the CDC.

To find a vaccination site near you, enter your zip code at Vaccines.gov.

Side Effects of COVID-19 Vaccines

So-called “adverse effects” of COVID-19 vaccination are rare, says the CDC, with the benefits of vaccination far exceeding the risks. These include:

  • Anaphylaxis (severe allergic reaction), occurring in approximately five people per million vaccinations
  • Myocarditis and pericarditis (inflammation of the heart muscle and heart lining) Cases have been linked to mRNA vaccines, with rates highest in men in their late teens and early twenties. People who experience these conditions generally respond well to medicine and rest and feel better quickly, says the CDC.

Rare conditions linked to the J&J vaccine, which is no longer available in the United States, include Guillain-Barré syndrome and thrombosis with thrombocytopenia syndrome (blood clots with low platelets).

Other Ways to Avoid Getting or Spreading COVID-19

In addition to vaccination, Mayo Clinic advises the following ways to protect yourself and those around you from COVID-19:

  • Avoid close contact with someone who tests positive for COVID-19 or has symptoms.
  • Keep distance between yourself and other people in crowded indoor spaces, especially if you are at high risk for severe COVID-19.
  • Avoid crowds and poorly ventilated indoor spaces.
  • Wash your hands often with soap and water, for at least 20 seconds, or use hand sanitizer with at least 60 percent alcohol.
  • Wear a face mask in indoor public spaces if you’re in an area where COVID-19 hospitalizations are high.
  • Improve indoor airflow through strategies such as opening a window.
  • Regularly clean and disinfect high-touch surfaces like doorknobs.
  • Stay home if you’re sick (unless you need medical care) and isolate yourself in your home to protect others in your household; avoiding sharing items like glassware, towels, and bedding.

Complications of COVID-19

COVID-19 can cause serious medical complications and even death. Although anyone can develop complications as a result of the virus, the risk is greater in older adults and people with existing medical conditions. Mayo Clinic lists the following as among the most common serious complications that arise with the disease:

  • Pneumonia and trouble breathing
  • Organ failure in several organs
  • Heart problems
  • Acute respiratory distress syndrome, a severe lung condition that causes a low amount of oxygen to go through your bloodstream to your organs
  • Blood clots
  • Acute kidney injury
  • Additional viral and bacterial infections

Multisystem Inflammatory Syndrome

Multisystem inflammatory syndrome (MISC) is a rare complication of COVID-19 that can affect children and adults. Multiple organs can become inflamed, including the heart, lungs, kidneys, brain, skin, eyes, or gastrointestinal tract. According to the CDC, symptoms include ongoing fever plus more than one of the following:

  • Stomach pain
  • Bloodshot eyes
  • Diarrhea
  • Dizziness or lightheadedness
  • Skin rash
  • Vomiting

Long COVID

Long COVID is generally defined as the persistence of COVID-19 symptoms, or the emergence of new health problems, four weeks or longer after the acute (initial) phase of COVID-19, says Yale Medicine.

According to a scientific investigation published in JAMA in May 2023, the top 12 symptoms of long COVID are:

  1. Post-exertional malaise (the worsening of symptoms following even minor physical or mental activity)
  2. Fatigue
  3. Brain fog
  4. Dizziness
  5. Gastrointestinal symptoms
  6. Heart palpitations
  7. Issues with sexual desire or capacity
  8. Loss of smell or taste
  9. Thirst
  10. Chronic cough
  11. Chest pain
  12. Abnormal movements

Research and Statistics: How Many People Have Had COVID-19?

According to the WHO, more than 770 million cases of COVID-19 have been confirmed globally and about 7 million deaths as of September 2023.

In the United States, COVID-19 has killed more than 1.1 million people and sent more than 6 million people to the hospital, according to the CDC.

COVID-19 and Racial and Ethnic Disparities

COVID-19 has had an outsize impact on communities of color in the United States, causing a disproportionate number of deaths.

A 2023 report from the Kaiser Family Foundation found that while the pandemic shaved 2.7 years off overall U.S. life expectancy between 2019 and 2021, people of color experienced the steepest declines, and long-standing health disparities worsened.

American Indian and Alaskan Native (AIAN) people lost 6.6 years in life expectancy, while life expectancy for Hispanic people and Black people declined 4.2 and 4 years, respectively, compared with a drop of 2.4 years for white people and 2.1 years for Asian people.

Editorial Sources and Fact-Checking

Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

Resources

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  • Symptoms of COVID-19. Centers for Disease Control and Prevention (CDC). October 16, 2022.
  • What Are the Most Common COVID-19 Symptoms? Zoe Health Study. December 13, 2022.
  • Coronavirus Disease (COVID-19): How Is It Transmitted? WHO. December 23, 2021.
  • About COVID-19. CDC. July 10, 2023.
  • COVID-19 Risks and Information for Older Adults. CDC. February 22, 2023.
  • COVID-19: People With Certain Medical Conditions. CDC. May 11, 2023.
  • Omicron, Delta, Alpha, and More: What to Know About the Coronavirus Variants. Yale Medicine. September 1, 2023.
  • What Is a Breakthrough Infection? Infectious Diseases Society of America. June 22, 2023.
  • COVID-19 Test Basics. U.S. Food and Drug Administration (FDA). September 9, 2023.
  • Long COVID or Post-COVID Conditions. CDC. July 20, 2023.
  • COVID-19 Treatments and Medications. CDC. May 26, 2023.
  • FDA Approves First Oral Antiviral for Treatment of COVID-19 in Adults. FDA. May 25, 2023.
  • Coronavirus Disease 2019 (COVID-19): Diagnosis and Treatment. Mayo Clinic. July 14, 2023.
  • Overview of COVID-19 Vaccines. CDC. September 12, 2023.
  • COVID-19 Vaccines for People Who Are Moderately or Severely Immunocompromised. CDC. September 12, 2023.
  • Selected Adverse Effects Reported After COVID-19 Vaccination. CDC. September 12, 2023.
  • Coronavirus Disease 2019 (COVID-19): Symptoms and Causes. Mayo Clinic. July 14, 2023.
  • Multisystem Inflammatory Syndrome (MIS). CDC. January 3, 2023.
  • Long COVID. Yale Medicine.
  • Thaweethai T, Jolley SE, et al. Development of a Definition of Postacute Sequelae of SARS-CoV-2 Infection. JAMA. May 25, 2023.
  • COVID Data Tracker. CDC. September 25, 2023.
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