News

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

covid-19 researchers

Malte Mueller / Getty Images

Key Takeaways

  • COVID-19 is primarily spread through the air by aerosols and respiratory droplets.
  • People with mild to moderate cases of SARS-CoV-2 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.

Countries worldwide are continuing to break records for confirmed COVID-19 cases. Some are instituting lockdowns, and many others are bracing for a combined flu and pandemic winter that experts predict could be the deadliest yet of this pandemic. Any efforts to slow down the pandemic hinge on understanding how COVID-19 spreads, how long people are contagious, and how long antibody protection lasts.

Since COVID-19 was first reported nearly a year ago, health experts have worked at breakneck speed to learn more about the disease, which is caused by the SARS-CoV-2 virus. More than 100 vaccines are being developed worldwide, and research papers—which can take more than a year to publish—are being published in weeks or months.

It’s easy to get confused by the deluge of findings and overwhelmed by the sheer volume of information from healthcare providers, researchers, public health experts, and governmental agencies—many of which you may have never heard of before. Here's a look at what we currently know about the contagiousness of COVID-19.

What This Means For You

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

How Does COVID-19 Spread?

According to the World Health Organization, COVID-19 is thought to primarily spread by respiratory droplets through close contact with an infected person after they sneeze, cough, or even speak. The virus can also spread by lingering on surfaces or objects.

Researchers agree most infections are likely spread through respiratory droplets from exposure to an infected individual at close range, within about 6 feet. Recent reports suggest that these particles may remain in the air for longer distances and be responsible for SARS-CoV-2 transmission in certain circumstances, such as in poorly ventilated enclosed spaces and during actions such as singing, shouting, or breathing heavily during exercise.

How Long Are People Contagious?

The Centers for Disease Control and Prevention (CDC) says that based on current evidence, people with mild to moderate COVID-19 are contagious for up to 10 days following symptom onset. Those who are immunocompromised may be contagious for up to 20 days.

The length of time people are thought to be contagious has changed over time, but the precautions to avoid catching or spreading the virus remain the same: As soon as people test positive or start showing symptoms, they need to self-isolate. That includes isolating from—or at least limiting contact and wearing a mask around—other household members.

If possible, infected people should sleep in a separate bedroom, use a separate bathroom, and frequently wipe down common surfaces. Everyone should try to limit their exposure and interactions with others outside the household as much as possible, too.

When Are People Most Contagious?

After studying COVID-19 transmission among 100 confirmed patients and their contacts in Taiwan last winter, researchers 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 symptomatic patients may not be enough to stop the spread of the virus.

The World Health Organization says that infected people appear to be most contagious two days before they develop symptoms.

Part of the challenge of stopping the spread of COVID-19 is that people can be asymptomatic or pre-symptomatic. If they are asymptomatic, that means they don't show symptoms while infected with SARS-CoV-2. If they are pre-symptomatic, that means they aren't showing any symptoms yet.

Without symptoms to alert them to their illness, it can be difficult for people to know they have COVID-19. Testing can sometimes be the only way to determine infection, and is important to pursue if you've been exposed to COVID-19.

Is COVID-19 Getting More Contagious?

Because of the way SARS-CoV-2 is mutating over time, the virus may be getting more contagious. But that doesn't mean more severe.

The culprit is a mutation on the virus's spike called D614G, which is associated with higher viral load. A person with a higher viral load is more infectious.

A study published on October 30 in the journal mBio shows the prevalence of D614G in 5,085 SARS-CoV-2 strains from patients in Houston, Texas. While the mutation was present in 82% of strains in March through May, it jumped to 99.9% of strains from May through July.

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

The short answer: yes. COVID-19 is a highly contagious disease, and stopping the spread means people with COVID-19 or people who have been exposed to need to distance.

The CDC says anyone who has had close contact with someone with COVID-19 should stay home for 14 days after their last exposure to that person.

However, there are exceptions. You don't need to stay home if you had COVID-19 illness within the previous three months and have recovered and are symptom-free.

Community and close contact exposures continue to be the main drivers of COVID-19. For a September CDC report, researchers assessed community and close contact exposures among those who tested positive and negative for COVID-19. Among those with COVID-19, 42% reported close contact with a person with COVID-19. Most close contact exposures were to family members. Only 14% of those who tested negative reported close contact with a person known to have COVID-19.

The CDC no longer requires a negative PCR test for people with mild to moderate cases to be declared clinically recovered. The decision of when it’s safe to stop self-quarantining or self-isolating is one that must be made in consultation with your healthcare provider and likely other members of your immediate household.

Are Clinically Recovered People Still Contagious?

Sometimes, people will continue to test positive for COVID-19 for weeks after their symptoms have cleared. Health experts still don’t know why—or exactly what that means for contagiousness.

"In some persons, after testing negative by RT-PCR [the most common diagnostic test] in two consecutive samples, later samples can test positive again," the CDC says. "It’s not possible to conclude that all persons with persistent or recurrent detection of SARS-CoV-2 RNA are no longer infectious. There is no firm evidence that the antibodies that develop in response to SARS-CoV-2 infection are protective."

A meta analysis of several studies found that people who have clinically recovered from COVID-19 do still have and can continue to shed (and spread) SARS-CoV-2 RNA. However, researchers have questions about the accuracy of the diagnostic tests involved in these studies.

In Korea, researchers have observed that recovered patients can continue to have detectable SARS-CoV-2 RNA for up to 12 weeks following clinical recovery.

 

Was this page helpful?
Article 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? Updated Oct. 20, 2020.

  2. Lerner AM, Folkers GK, Fauci AS. Preventing the spread of SARS-CoV-2 with masks and other “low-tech” interventions. JAMA. Published online October 26, 2020. doi:10.1001/jama.2020.21946

  3. Centers for Disease Control and Prevention. Clinical Questions about COVID-19: Questions and Answers. Updated Nov. 4, 2020.

  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. Long SW, Olsen RJ, Christensen PA, Bernard DW, et al. Molecular architecture of early dissemination and massive second wave of the SARS-CoV-2 virus in a major metropolitan area. mBio. doi.10.1128/mBio.02707-20

  6. Centers for Disease Control and Prevention. When You Can be Around Others After You Had or Likely Had COVID-19. Updated Oct. 27, 2020.

  7. Fisher KA, Tenforde MW, Feldstein LR, et al. Community and close contact exposures associated with COVID-19 among symptomatic adults ≥18 Years in 11 outpatient health care facilities - United States, July 2020. MMWR Morb Mortal Wkly Rep. 2020;69(36):1258-1264. Published 2020 Sep 11. doi:10.15585/mmwr.mm6936a5

  8. Dao TL, Hoang VT, Gautret P. Recurrence of SARS-CoV-2 viral RNA in recovered COVID-19 patients: a narrative review. Eur J Clin Microbiol Infect Dis. 2020. doi:10.1007/s10096-020-04088-z

  9. Korea Disease Control and Prevention Agency. Findings from investigation and analysis of re-positive cases. Updated June 3, 2020.