How Long Is COVID-19 Contagious? A Look at the Research

covid-19 researchers

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Key Takeaways

  • COVID-19 is primarily spread through the air.
  • People with mild to moderate cases of COVID-19 are thought to be contagious for up to 10 days.
  • People who test positive for COVID-19 or who have been in close contact with people who have COVID-19 should self-quarantine. Vaccinated people who have been in close contact with someone with COVID-19 don't have to quarantine, but should be tested.

To prevent COVID-19, it's important to know:

COVID-19 is caused by the SARS-CoV-2 virus.

The information we have about COVID-19 is always evolving. New variants may be more contagious than the current dominant strains. This is why it is important to know how the virus spreads, so you can avoid passing it on to others.

This article looks at what we know about the contagiousness of COVID-19.

What This Means For You

COVID-19 is a very contagious disease. Knowing how the SARS-CoV-2 virus spreads and how long it stays in your system is important. This can help reduce your likelihood of catching COVID-19 or passing it to a loved one.

How Does COVID-19 Spread?

According to the World Health Organization (WHO), the primary way COVID-19 spreads is through respiratory droplets. These are small particles that stay in the air after a person sneezes, coughs, or speaks.

When you have close contact with an infected person, you may inhale these droplets or get them in your mouth, nose, or eyes.

The virus can also spread when you touch a contaminated surface or object.

Research suggests that most of the spread happens at close range, within about 6 feet. There is also evidence that particles can travel longer distances in the air.

In certain circumstances, these airborne particles may also transmit SARS-CoV-2. These means the virus may spread more easily in places with poor ventilation. Activities like singing, shouting, or breathing heavily during exercise may also increase the distance the virus can travel.

How Long Are People Contagious?

The Centers for Disease Control and Prevention (CDC) says most people with COVID-19 are contagious for up to 10 days following symptom onset. Symptom onset is the day you first start to feel sick.

People who have had severe COVID-19 may be contagious for up to 20 days. This is also true for people who are immunocompromised. Immunocompromised people have immune systems that don't function well.

Self-isolate as soon as you have tested positive for COVID-19 or start having symptoms. This means staying home. It also means isolating from other members of your household, or limiting contact and wearing a mask at home.

If possible, infected people should sleep in a separate bedroom. If you have COVID-19, use a separate bathroom and wipe down common surfaces.

Everyone in the house should try to limit their exposure. As much as possible, household members who are not sick should avoid interactions with people outside the home.

COVID-19 is very contagious. You can pass it to others even if you have mild or no symptoms. It is important to self-isolate as soon as you start to feel sick.

When Are People Most Contagious?

A 2020 study looked at COVID-19 transmission among 100 confirmed patients and their contacts in Taiwan. The study found that most transmission occurred at the very early stage of the disease, or even before the onset of symptoms.

This suggests that finding and isolating patients who have symptoms may not be enough to stop the spread of the virus.

The World Health Organization says infected people appear to be most contagious two days before they develop symptoms, and just afterwards.

People with COVID-19 can be asymptomatic or pre-symptomatic. An asymptomatic person is infected with SARS-CoV-2 but has no symptoms. A pre-symptomatic person is infected but isn't showing symptoms yet.

This is one reason why it is so difficult to stop the spread of COVID-19. If you don't have symptoms, you may not know you have COVID-19. Sometimes the only way to know is to get tested. This is why it's important to get tested if you've been exposed to someone with COVID-19.

Is COVID-19 Getting More Contagious?

The SARS-CoV-2 virus mutates over time. The delta variant is more contagious than the original form of SARS-CoV-2. This is because it is associated with higher viral load.

Viral load is the amount of virus that's in your body. A person with a higher viral load is more contagious.

New variants may also prove to be more contagious. This does not necessarily mean they will be more severe.

Do People Who Have Been Around Someone With COVID-19 Need to Self-Quarantine?

The short answer is yes. COVID-19 is highly contagious. To stop the spread, people with COVID-19 or who have been exposed to COVID-19 need to distance themselves from others.

The CDC says anyone who has had close contact with someone with COVID-19 and is not fully vaccinated should stay home for 14 days after their last exposure to that person.

Close contact means you have been within 6 feet of someone with COVID-19 for 15 minutes or more over a period of 24 hours. 

If you are fully vaccinated, you still need to be careful. Get a COVID-19 test five to seven days after your last contact with the infected person. Wear a mask indoors for at least 14 days after your exposure, or until you receive a negative test result.

You also do not need to stay home if you had COVID-19 within the previous three months and have recovered and are symptom-free.

Community and close contact exposures are still the main drivers of COVID-19. Transmission is most likely indoors. Workplaces with lots of people who spend many hours together have high rates of transmission. Transmission is also high within households.

The CDC used to require a negative PCR test before people who have had mild to moderate cases could stop self-isolating. A PCR test looks for the genetic material of the SARS CoV-2 virus.

The CDC no longer requires this test. Instead, you, your doctor, and other members of your household should decide together when it is time to stop self-isolating.

Are Clinically Recovered People Still Contagious?

Sometimes, people will continue to test positive for COVID-19 for weeks after they no longer have symptoms. Health experts still don’t know why.

The CDC says these people are unlikely to be contagious. Studies have not found any evidence that people who have recovered from COVID-19 can pass it on to others.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

7 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. World Health Organization. Coronavirus disease (COVID-19): How is it transmitted?

  2. Lerner AM, Folkers GK, Fauci AS. Preventing the spread of SARS-CoV-2 with masks and other “low-tech” interventions. JAMA. doi:10.1001/jama.2020.21946

  3. Centers for Disease Control and Prevention. Clinical Questions about COVID-19: Questions and Answers.

  4. Cheng H, Jian S, Liu D, et al. Contact tracing assessment of COVID-19 transmission dynamics in taiwan and risk at different exposure periods before and after symptom onset. JAMA Intern Med. 2020;180(9):1156–1163. doi:10.1001/jamainternmed.2020.2020

  5. Centers for Disease Control and Prevention. Quarantine and isolation.

  6. O’Keeffe J, Eykelbosh A. National Collaborating Centre for Environmental Health. Understanding transmission of SARS-CoV-2 in the ongoing COVID-19 pandemic.

  7. Centers for Disease Control and Prevention. Ending isolation and precautions for people with COVID-19: interim guidance.

By Nicole Stempak
Nicole Stempak, MS, writes for patients, physicians, and healthcare administrators. She previously served as editor of Physicians Practice.