Do We Know if Asymptomatic Carriers Spread Coronavirus?

Analysis by Dr. Joseph Mercola


  • An article published January 30, 2020, stated asymptomatic people could spread SARS-CoV-2; the data have since been refuted
  • The researchers published the paper without confirming the facts with the businesswoman who spread the virus; it was later found that she did have symptoms
  • Testing 263 people in South Korea who recovered from COVID-19 revealed positive results; however, the test used identified the presence of virus genetic material but not if the virus was living
  • Nasal swabs identify genetic material from the virus and blood tests identify antibodies developed after an infection; both tests are available
  • Some countries are gearing up to issue “immunity passports,” indicating people have antibodies and may return to work or travel

Coronaviruses are a common infection in people and animals. To date, the Centers for Disease Control and Prevention believes the main mode of transmission for SARS-CoV-2 is from person to person, specifically through respiratory droplets.1 These are most often produced when an infected person coughs or sneezes.

However, the virus may also be aerosolized when a person speaks. Experts believe that the louder you speak, the more likely it is you’ll spit. Although transmission has not been tracked to objects and surfaces, the CDC recommends cleaning and disinfecting frequently used objects in your home.

It is estimated that the most contagious period is when a person is sickest and symptomatic. The length of time an individual remains sick is specific to an individual situation such as their age, vitamin D levels and immune system. Although it may be possible to catch the virus by touching a surface and then touching your mouth, nose or eyes, it doesn’t live long on surfaces.

The CDC estimates the likelihood of transmission from food products or packaging is low. Additionally, any virus on food is killed during cooking and preparation. Experts hope that higher temperatures and humidity levels during the summer months will slow the spread of the virus.

Can You Spread COVID-19 Without Having Symptoms?

January 30, 2020, an article was published in The New England Journal of Medicine2 in which the author proposed the transmission of COVID-19 is possible from an asymptomatic carrier.

The writers reported a 33-year-old businessman had met with his business partner from Shanghai between January 19 and 22, 2020. January 24, 2020, the businessman developed a fever and productive cough. The next evening, he felt better and went back to work January 27.

The writers reported the partner had been “well with no signs or symptoms of infection, but had become ill on her flight back to China, where she tested positive for 2019-nCoV on January 26.” From this case study they theorized the virus could be transmitted from asymptomatic carriers.

While some infections spread from asymptomatic individuals, there is not enough evidence yet to suggest that COVID-19 does. But, as it turns out, in their zeal to get the paper published, the researchers did not speak with the partner from Shanghai before publication. They relied on information from the people with whom she met who said she “did not appear to have any symptoms.”3

Unfortunately, this information has been quoted often, has made many headlines and may have had an impact on public health guidelines. In fact, Dr. Anthony Fauci, director of the U.S. National Institute of Allergy and Infectious Diseases, told journalists,4 “There’s no doubt after reading [the NEJM] paper that asymptomatic transmission is occurring. This study lays the question to rest.”

Accurate Information Needed for Public Health Policy

Looking into the matter further, Germany’s public health agency, the Robert Koch Institute (RKI), sent a letter with accompanying information to set the record straight. RKI did speak with the woman on the phone, and she reported she did have symptoms while in Germany.

The Health and Food Safety Authority from Bavaria was also on the phone call. Science reports one of the authors spoke with the Bavarian Health and Food Safety Authority and asked if the information shared from the woman required a correction to the article. He was assured it did not.

Yet, as Science reports, RKI did not agree and sent a letter to The New England Journal of Medicine, the World Health Organization and European partner agencies with the information.

Some experts were charitable in their description of what happened, such as an epidemiologist from Harvard T.H. Chan School of Public Health who called it a “poor choice” and assumed it “was an overstretched group trying to get out their best idea of what the truth was quickly, rather than somebody trying to be careless.”5

Others were not quite so forgiving, such as the Public Health Agency of Sweden, which the Science Chronicle reported updated their website’s FAQ page with the following information:6

“The sources that claimed that the coronavirus would infect during the incubation period lack scientific support for that analysis in their articles. This applies, among other things, to an article in NEJM that has subsequently proven to contain major flaws and errors. Statements by the Chinese authorities on infectiousness during the incubation period lack sources or other data to support it.”

False Positive Tests in People Who Recovered

South Korea tested 263 people who had recovered from COVID-19, yet who tested positive again in the days and weeks after full recovery.7 The information shone a light on questions of whether people could get reinfected or if the infection could be reactivated.

However, the scientist who leads the clinical committee for emerging disease control believes the test detected dead virus fragments and not a live virus. The committee believes there is little reason to think individuals could be reinfected or that an infection could be reactivated.

This, of course, would have a significant impact on global efforts to contain the SARS-CoV-2 virus. The individuals were tested with a polymerase chain reaction (PCR) test used to diagnose COVID-19 and to trace the genetic material of the virus.

This test does not delineate between fragments taken from dead cells or from a live virus. Scientists are finding the dead fragments from SARS-CoV-2 can take months to clear after an individual has recovered from the infection and thus can lead to false positives with a PCR test.

The committee confirmed an earlier finding that patients who seem to have a repeat infection have little to no contagiousness. This is likely from the results of testing identifying dead cell fragments and not the live virus. Oh Myoung-don, who leads the Central Clinical Committee for Emerging Disease Control, said:8

“The process in which COVID-19 produces a new virus takes place only in host cells and does not infiltrate the nucleus. This means it does not cause chronic infection or recurrence.”

How long the virus is infectious will be key to determining public health policy regarding the amount of time quarantine for an infected person should be recommended. Bloomberg9 reports past studies had shown those who were severely ill remain infectious longer than those who may have had a mild illness.

PCR Does Not Test for Live Viruses

The types of testing used to determine if someone has COVID-19 is a rapidly evolving process. The timeline began on January 11 when scientists from China posted the genome of the novel coronavirus. One week later Germany had produced a diagnostic test.

By the end of February, the WHO sent tests to nearly 60 countries, but the U.S. refused.10 This slowed the release of a test that might have helped track the spread of the virus. The initial efforts in the U.S. were fraught with challenges. The first tests developed by the CDC didn’t work and the FDA did not create an avenue for medical centers to produce their own tests.

The first coronavirus tests were PCR tests that work by essentially photocopying molecules to magnify small segments of DNA material.11 This allows scientists to map the DNA, detect the presence of bacteria or viruses and diagnose genetic disorders. When used for SARS-CoV-2, it can identify the presence of the genetic material from the virus, but not whether the virus is currently living.

PCR testing for COVID-19 was done by inserting a swab through the nose to the nasopharyngeal area where the nose and throat meet. The swab is rotated for 15 seconds and then the procedure is repeated in the other nostril to ensure an adequate sample is obtained.12

However, in taking steps to speed testing, the FDA changed their recommendations in mid-April so samples could be collected inside the nose instead of the pharyngeal area.13 Additionally, they also are allowing sample collection by patients themselves, and storage using saline solution instead of being stored in a viral transport medium, which is in short supply.

What Else May Be Holding Up Testing?

Two of the bottlenecks to having enough testing available have been a shortage of PCR machines and appropriate swabs. Cotton swabs cannot be used since cotton is a plant and has its own DNA that would contaminate the test.

In mid-April, months after other countries had been testing their citizens in mass numbers, the FDA opened the door for different types of swabs to be used. The FDA commissioner released a statement congratulating the administration for its action:14

“This action today demonstrates the ingenuity that results from FDA working in partnership with the private sector. The Trump Administration has been working side-by-side with our industry partners to fight this pandemic, and today is a great example of that work.”

Another advancement in testing came when Abbott Laboratories produced a rapid test, which they made available throughout the U.S. and which was distributed by the federal government. CNN reports the lab has instructed health care professionals not to use viral transport media for the samples intended for the ID NOW device.15

This device tests one swab at a time and can complete a test in as quickly as five minutes. The customer should only use swabs that have not been placed in any solution. When the viral transport media is used, the device produces false negatives.

Clinical pathologists from Cleveland Clinic tested five systems, processing approximately 200 samples. They found that when used correctly, the ID NOW detected only 84.4% of the positive specimens. The CDC16 has also developed a blood test which looks for antibodies. These antibodies are specific proteins your body produces in response to an infection.

People who have had COVID-19 have antibodies in the blood that indicate they’ve had an immune response to the infection. Despite the presence of antibodies, the CDC is still unsure if these provide immunity to a second exposure or how high the antibody titer must be to provide protection.

United Nations Warns Don’t Issue Immunity Passports

At the end of April, the WHO was still unsure if those who have recovered from COVID-19 will have enough antibodies to protect them from the second infection. The United Nations has warned governments around the world against issuing any immunity passports or risk-free certificates.

Governments hope these documents can be used to allow free travel throughout the world, demonstrating that those who carry them are not a risk to others. Taking a more conservative approach, WHO released a statement:17

“Some governments have suggested that the detection of antibodies to the SARS-CoV-2, the virus that causes COVID-19, could serve as the basis for an ‘immunity passport’ or ‘risk-free certificate’ that would enable individuals to travel or to return to work assuming that they are protected against re-infection. There is currently no evidence that people who have recovered from COVID-19 and have antibodies are protected from a second infection.”

At the time of the April 25, 2020, press release from the WHO, Chile had announced they would begin handing out health passports after screening individuals who had developed antibodies so they could go back to work. In a news report May 6, 2020, on NBC News, Chili’s Ministry of Health continued to stand by their decision.18

They announced they would be issuing certificates in the form of a QR code to those who had been clear of symptoms of the virus for 14 days. In Germany, experts are conducting swab tests numbering nearly 100,000 per day in the hope of providing certificates to those who test negative.

Italy is also issuing licenses to people with antibodies and China is moving ahead with a similar system. Glenn Cohen is a bioethicist from Harvard University who is concerned that some may look to counterfeit practices to get an immunity badge. He told NBC News:19

“I’m really worried about the diverting of resources which are finite to cracking down on the black market rather than have these resources aimed at the interventions that are most efficacious in curbing infection and helping people survive.”