Fact check: Yes, asymptomatic infections are real

The claim: Asymptomatic infections are actually ‘healthy’ people

Asymptomatic transmission of the coronavirus has been called a silent driver of the COVID-19 pandemic, but a post shared thousands of times on Instagram claims infections without symptoms aren’t real.

The June 7 post claims asymptomatic infections are actually “healthy” people and calls instances of people who test positive for the virus but show no symptoms a “false positive.” It has been shared more than 5,000 times.

Contrary to the post’s claims, experts say asymptomatic infections are real, though pinpointing the breadth of those cases is complicated.

The user who shared the post did not respond to a request for comment.

Tests, studies show asymptomatic infections

People who are infected but not showing symptoms are less likely to pursue testing. But PCR testing has shown evidence of asymptomatic infections, said Dr. Ellen Foxman, assistant professor at the Yale School of Medicine. 

“We don’t know exactly (how prevalent asymptomatic infections are), since we haven’t tested most of the population,” Foxman said in an email to USA TODAY. 

Some research has pegged the rate of asymptomatic infections between 17% and 81%, according to a November article in the journal Nature. 

Foxman said PCR tests using a nasal swab have returned as positive in people who showed no symptoms. Other experts agreed false positives are rare with PCR testing.

For example, Foxman said the hospital at Yale used PCR tests to screen patients on admission and before sending residents of nursing homes back to their facilities. Workplaces and colleges also used PCR tests to screen people, she said.

“Sometimes, people tested positive for COVID-19 but felt perfectly fine,” she said. “This is an asymptomatic infection.”

Contact tracing also has picked up asymptomatic cases, she said.

“Asymptomatic COVID-19 definitely happens,” Dr. Matthew Laurens, associate professor at the University of Maryland School of Medicine, said in an email to USA TODAY.

Vaccine studies and other clinical trials have turned up asymptomatic infections “as part of routine study procedures,” he said.

Studies have shown people who are infected but asymptomatic can spread the virus, and the CDC has continued to recommend that unvaccinated people take precautions such as mask-wearing and social distancing to prevent infections.

An analysis of 94 COVID-19 studies estimated about 20% of people who become infected will remain asymptomatic throughout the infection. The analysis was published in September 2020 in the journal PLOS Medicine.

Another review, published in May in the journal Annals of Internal Medicine, found at least a third of infections are asymptomatic. Researchers reviewed 61 studies and reports for the analysis.

Fact check: Peer-reviewed studies have shown safety, efficacy of COVID-19 vaccines

A study published in May 2020 in the New England Journal of Medicine surveyed 76 residents of a skilled nursing facility. Of those, 48 tested positive for COVID-19, and 27 were asymptomatic at the time of the test. All but three of the asymptomatic infections later developed symptoms.

Some asymptomatic people feel effects later

Experts interviewed by USA TODAY distinguished between asymptomatic infections, where symptoms never developed, and those that were “presymptomatic,” meaning they developed symptoms later.

“Anyone who has been infected with the virus that causes COVID-19, regardless of age, can be contagious and spread the infection to others starting 48 hours (or 2 days) before the person has any symptoms or tests positive,” Jasmine Reed, a CDC spokeswoman, said in an email to USA TODAY.

University of Chicago researchers used a mathematical model to determine that about 50% of community transmission in New York City during the early stages of the pandemic was from asymptomatic and presymptomatic cases. The research was published in February in the Proceedings of the National Academy of Sciences.

While the post claims asymptomatic infections have never been classified as positive cases with other illnesses, experts said that isn’t true.

“There’s great data on asymptomatic influenza causing transmission and other respiratory viruses,” Dr. Allison Bartlett, associate medical director of the pediatric infection control program at UChicago Medicine, told USA TODAY.

Many viruses can replicate in humans and not cause symptoms, including enteroviruses, human polio virus, human papilloma virus and others, Laurens said.

“The situation is not unique to SARS-CoV-2,” he said.

June 17, 2021: Bravo, a Labrador Retriever, sits in front of a sample of human sweat after detecting the COVID-19 coronavirus at a mobile canine unit in Bangkok. Thailand has deployed a canine virus detection squad to help provide a fast and effective way of identifying people with COVID-19 as the country faces a surge in cases, with clusters found in several crowded slum communities and large markets. (Photo: Sakchai Lalit, AP)

Our rating: False

The claim that asymptomatic infections are actually healthy people is FALSE, based on our research. Experts and an array of studies have confirmed the virus can spread from people who are infected but not showing symptoms of COVID-19. The post also claims asymptomatic cases are false positives, but experts agreed false positives from PCR tests are rare.

Our fact-check sources:

  • U.S. News & World Report, July 7, 2020, Study: ‘Silent’ Transmission the Top Driver of COVID Outbreak
  • Ellen Foxman, May 14, email interview with USA TODAY
  • Nature, Nov. 20, 2020, What the data say about asymptomatic COVID infections
  • Allison Bartlett, May 14, phone interview with USA TODAY
  • Matthew Laurens, May 14, email interview with USA TODAY
  • PLOS Medicine, Sept. 22, 2020, Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis
  • Annals of Internal Medicine, May, The Proportion of SARS-CoV-2 Infections That Are Asymptomatic
  • The New England Journal of Medicine, May 28, 2020, Presymptomatic SARS-CoV-2 Infections and Transmission in a Skilled Nursing Facility
  • Jasmine Reed, June 15, email interview with USA TODAY
  • UChicago Medicine, May 11, Asymptomatic coronavirus infections contribute to over 50% of spread, according to UChicago study
  • The Associated Press, June 10, Asymptomatic COVID-19 infections do occur

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Our fact check work is supported in part by a grant from Facebook.

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