A New Study Proves This Type of COVID Transmission Is Not Rare
Researchers found that asymptomatic people carry just as much of the virus as those with symptoms.
Early in June, a COVID news briefing from the World Health Organization (WHO) led to pushback from the global medical community, when Maria Van Kerkhove, PhD, head of WHO's Emerging Diseases and Zoonosis Unit, said that it is "rare that an asymptomatic person actually transmits [the virus] onward." The next day, she expanded on that comment, saying that there is much "unknown" about coronavirus transmission. Now, a new study published in JAMA Internal Medicine confirms that asymptomatic individuals are responsible for transmitting the coronavirus. In fact, they carry just as much of the virus as those who experience symptoms.
The study, conducted by researchers in South Korea, aimed to discover whether there was a difference in viral load carried by asymptomatic and symptomatic COVID patients. Looking at just over 300 people living in isolation in a treatment center, the study determined that, when it comes to the amount of virus that they carry, "values in asymptomatic patients were similar to those in symptomatic patients." As the viral load makes even asymptomatic patients capable of infecting others, "isolation of asymptomatic patients may be necessary to control the spread of SARS-CoV-2," the study states.
Speaking to The New York Times, Tufts University virologist Marta Gaglia, PhD, said that the fact that this study was conducted over a long period of time makes it a particularly meaningful one as it pertains to asymptomatic spread. "When they talk about asymptomatic patients, they really, really know that these were true asymptomatics," she said. (Out of the 303 patients monitored, 30 percent never developed any symptoms.) The doctor, who was not involved in the South Korea research, also said that, in light of these conclusions, "there's no actual reason to believe a priori that [asymptomatic people] would transmit any differently" than COVID patients who do experience symptoms.
The researchers in South Korea did find that asymptomatic individuals were rid of the virus around the 17th day after exposure, while sick patients retained it for two or three days more. However, it is still unclear for how long exactly infected individuals are contagious.
Among the limitations the researchers noted in their paper are the fact that the patients in the study were all young and relatively healthy and therefore don't represent the whole population. Also, their participants did not account for any false-negative test results. Beyond that, the study only tested viral load and not direct transmission, seeing as all participants were isolated whether or not they had symptoms. "We did not determine the role that molecular viral shedding played in transmission from asymptomatic patients," they conclude.
Still, the results suggest that asymptomatic people are capable of infecting others, perhaps to the same degree as sick patients. In a live-streamed Facebook Q&A on July 16, Anthony Fauci, MD, director of National Institute of Allergy and Infectious Diseases (NIAID), said: "What we have found is that when you measure the level of virus in the nasal pharynx of asymptomatic people compared to people who are symptomatic, there doesn't seem to be any difference. Which means there's as much virus in the nose of a person who's asymptomatic as there is in a symptomatic person. Which means it is very, very likely, when that person talks or sneezes or whatever, that enough virus will come out to infect someone else. So there is not a lot of difference in virus load, even though people can be very different with regard to their symptoms."
As a result of the potential power of asymptomatic spread, researchers advise that post-exposure quarantine may be essential across the board in order to slow the spread of COVID. And for more on the variations in the virus, This Is Why COVID Kills Some People and Others Are Symptom-Free, Study Says.