Asymptomatic people with COVID-19 are just as contagious as those showing symptoms, key study finds

In a new study of over 300 COVID-19 patients in South Korea, researchers have found that those with and without symptoms are equally likely to transmit the SARS-CoV-2 coronavirus. They found roughly the same amounts of SARS-CoV-2 virus in the noses, mouths and lungs of asymptomatic COVID-19 patients as they did in others with cough and fever.

The researchers studied 303 patients, with a median age of 25, that were in isolation at a treatment facility in Cheonan, South Korea. The participants were all isolated when they tested positive for the virus, and were monitored for symptoms of COVID-19 like fever, as well as how much virus was in their sputum — an indication of the lungs in the nose, throat and lungs.

Based on their findings, reported in JAMA Internal Medicine, the researchers suggest that infected people should be isolated regardless of how weak or severely the external symptoms of COVID-19 manifest.

The study offers evidence in the consequential debate about how contagious asymptomatic COVID-19 patients really are. Currently, most health experts working around COVID-19 are doing so with the notion that symptomatic people are more contagious.

There’s been this big question pretty much since January, since data started coming out of China, about people that were asymptomatic or pre-symptomatic," Jason Kindrachuk, a virologist at the University of Manitoba told the New York Times. "What we haven’t really had any clue of yet is what role people who are asymptomatic play in transmission of disease."

Travellers with masks walk on a railway platform in Pune August 18, 2009. Pune has reported the highest number of deaths caused by H1N1 influenza virus in India, according to a government statement released on Monday. Reuters

There has also been much debate and confusion around the two subgroups that fall under the COVID-19 "asymptomatics"  category – the "pre-symptomatic" group that is infected but yet to manifest symptoms, and the "asymptomatic" who seem healthy throughout the course of a COVID-19 infection.

The difference between these two camps is highlighted by the researchers for the first time in such a large study – truly asymptomatic people shed as much virus from their nose, throat and lungs, and for almost as long, as symptomatic COVID-19 patients.

Since asymptomatic patients contained as much of the virus in their noses and throats, they were just as likely to spread the infection – a finding that has important consequences in guidelines and policymaking around COVID-19 transmission and prevention.

"The real strength of the study is, they have a very large number of patients, and they have very good follow-up," Marta Gaglia, a virologist at Tufts University in Massachusetts who was not involved in the work told NYT.

The findings emphasize the importance of ramping up testing and contact tracing so people without symptoms can isolate sooner, and stop the chain of transmission. This is a concern in many countries including India, where the number of new cases being reported every day is in fluctuation, but overall, still on the rise.

 

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