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Madison Czopek
By Madison Czopek May 17, 2021

COVID-19 can be transmitted by people without symptoms

If Your Time is short

• Multiple studies have concluded that individuals who test positive for COVID-19 can transmit the virus to others, even if they show no symptoms.

• There is no consensus estimate on how frequently asymptomatic people transmit the virus to others.

After more than a year of advising strict COVID-19 safety guidelines, the U.S. Centers for Disease Control and Prevention announced May 14 that fully vaccinated individuals can resume most regular activities without wearing masks or social distancing. 

Many people, including President Joe Biden, viewed the news as a positive sign, but some social media users interpreted the change differently. 

"This week we learned the CDC lied about outdoor transmission, which helped shape COVID prevention measures across states," reads one Instagram post. "What makes anyone think they haven’t lied about almost everything including transmission by asymptotic people, aka healthy people."

The caption on the post — which again erroneously uses the mathematical term "asymptotic" instead of the medical term "asymptomatic" — continues: "Transmission by asymptotic people has never been proven, which is how they shaped the entire policy around this issue." 

The post was flagged as part of Facebook’s efforts to combat false news and misinformation on its News Feed. (Read more about our partnership with Facebook.)

Setting aside the improper terminology, the post’s claim is false.

Studies have found that COVID-19 can be spread by people who are asymptomatic and do not show any symptoms of the disease. 

In a June 2020 interview on "Good Morning America," Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, estimated that 25% to 45% of "of the totality of infected people likely are without symptoms."

During the same interview, Fauci said, "we know from epidemiological studies" that asymptomatic people can transmit the virus "to someone who is uninfected even when they’re without symptoms."

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While not all researchers agree on exactly how or how frequently asymptomatic transmission happens, multiple studies have concluded that it does happen. 

A study conducted in Singapore from January to March 2020 found that presymptomatic transmission was responsible for several clusters of COVID-19 cases. For the purposes of the study, presymptomatic transmission was defined as "the transmission of SARS-CoV-2 from an infected person (source patient) to a secondary patient before the source patient developed symptoms ...with no evidence that the secondary patient had been exposed to anyone else with COVID-19."

Another study conducted at a skilled nursing facility in Washington found that "live coronavirus clearly sheds at high concentrations from the nasal cavity even before symptom development. Experts who analyzed the study concluded that the results indicated "that asymptomatic persons are playing a major role in the transmission of SARS-CoV-2."

Additional studies in The Journal of the American Medical Association, Science China Life Sciences, PLOS Medicine and Clinical Microbiology and Infection reaffirmed that asymptomatic transmission of COVID-19 occurs — though they generally conclude that it occurs less frequently than symptomatic or presymptomatic transmission. 

The updated CDC guidance is for vaccinated people. The CDC explained the change on its website: "A growing body of evidence suggests that fully vaccinated people are less likely to have asymptomatic infection and potentially less likely to transmit SARS-CoV-2 to others. However, further investigation is ongoing."

The CDC also cited a broader need to encourage vaccination in its rationale for changing masking and social distancing requirements for fully vaccinated people. It referenced a January 2021 Kaiser Family Foundation survey about COVID-19 vaccine hesitancy.

"Maintaining a requirement to continue all prevention measures after vaccination may disincentivize vaccine uptake," the CDC’s website says. "In a survey from January 2021, one in five people reported being less likely to get vaccinated if they heard that they will need to continue to wear a mask and practice social distancing even after getting vaccinated."

Our ruling

An Instagram post claimed that transmission of COVID-19 by people who are asymptomatic "has never been proven."

Multiple studies have found that asymptomatic transmission of COVID-19 occurs, though there is no consensus on how or how often it happens. 

We rate this claim False.

Our Sources

Instagram post, May 13, 2021

U.S. Centers for Disease Control and Prevention, "When you’ve been fully vaccinated," accessed May 16, 2021

The Boston Globe, "‘Today is a great day for America,’ Biden says, as CDC eases mask guidelines," May 13, 2021

UC Health, "The truth about COVID-19 and asymptomatic spread: It’s common, so wear a mask and avoid large gatherings," Nov. 5, 2020

CNN, "Iceland lab's testing suggests 50% of coronavirus cases have no symptoms," April 3, 2020

Johns Hopkins University Hub, "Asymptomatic Spread Makes COVID-19 Tough To Contain," May 12, 2020

U.S. Centers for Disease Control and Prevention, "Presymptomatic Transmission of SARS-CoV-2 — Singapore, January 23–March 16, 2020," April 10, 2020 

Hartford Healthcare, "30 Percent of People With COVID-19 Show No Symptoms: Here’s Where They Carry It," Nov. 23, 2020

CNBC, "Dr. Anthony Fauci says WHO’s remark on asymptomatic coronavirus spread ‘was not correct,’" June 10, 2020

PolitiFact, "WHO comment sparks ‘I-told-you-so’ about coronavirus spread," June 11, 2020

Good Morning America YouTube, "Fauci calls coronavirus his 'worst nightmare' as cases spike l GMA," June 10, 2020

U.S. Centers for Disease Control and Prevention, "Evidence Supporting Transmission of Severe Acute Respiratory Syndrome Coronavirus 2 While Presymptomatic or Asymptomatic," July 2020

The New England Journal of Medicine, "Asymptomatic Transmission, the Achilles’ Heel of Current Strategies to Control Covid-19," April 24, 2020

The New England Journal of Medicine, "Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility," April 24, 2020

Nature, "What the data say about asymptomatic COVID infections," Nov. 18, 2020

AZCentral, "Yes, it's possible to catch COVID-19 from someone without symptoms. Here's what you need to know," June 12, 2020

PolitiFact, "No, a recent study didn’t find that there was "no asymptomatic" spread of COVID-19," Dec. 28, 2020

Journal of the American Medical Association, "Presumed Asymptomatic Carrier Transmission of COVID-19," Feb. 21, 2020

Science China Life Sciences, "Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China," March 4, 2020

PLOS Medicine, "Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis" Sept. 22, 2020

Clinical Microbiology and Infection, "Defining the role of asymptomatic and pre-symptomatic SARS-CoV-2 transmission – a living systematic review," Oct. 6, 2020

U.S. Centers for Disease Control and Prevention "Science Brief: Background Rationale and Evidence for Public Health Recommendations for Fully Vaccinated People," accessed May 17, 2021

Kaiser Family Foundation, "KFF COVID-19 Vaccine Monitor: January 2021," Jan. 22, 2021

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