Asymptomatic Coronavirus Carriers May Be As Contagious As Those With Symptoms, Study Finds

TOPLINE

As debates over when and how to safely reopen schools and businesses rage, a South Korean study published Thursday by JAMA Internal Medicine confirms what many health experts had assumed and feared, that coronavirus carriers who don't exhibit any symptoms are capable of spreading the virus.

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KEY FACTS

South Korean scientists analyzed samples taken from 303 people isolated at a community treatment center who had tested positive for the coronavirus between March 6 and 26.

Of the 303, 193 were symptomatic when they were isolated and 110 were asymptomatic, and researchers found that the viral loads (the amount of virus in an infected person) were very similar in both types of patients.

According to the New York Times, this result "offers more definitive proof that people without symptoms carry just as much virus in their nose, throat and lungs as those with symptoms, and for almost as long."

Individuals who feel perfectly fine but are still capable of spreading Covid-19 have been a primary concern among those advocating against fully reopening schools for in-person learning and rushing to reopen businesses.

"It's important data, that's for sure," Benjamin Cowling, an epidemiologist at the University of Hong Kong who was not involved in the work, told the New York Times. "And it does confirm what we've suspected for a long time — that asymptomatic cases can transmit infection."

Of the initially asymptomatic patients, 89 did not exhibit any outward symptoms throughout the quarantine (representing 29.3% of the total), while less than 7% eventually developed symptoms.

Key Background:

South Korean scientists acknowledge the study contains significant limitations. First and foremost, the participants were mostly young, with a median age of just 25. The study also mentions that only testing people who have symptoms could result in "substantial underreporting of infected patients." Despite the presence of similar viral loads, Cowling told the New York Times that because asymptomatic people do not frequently cough or sneeze, they may be "less efficient at expelling the virus than those who are clearly unwell." Conversely, Marta Gaglia, a virologist at Tufts University in Massachusetts, said individuals who feel ill often remain inside, resting in bed, "whereas the infected but unaware may carry on with their business, sickening others along the way."

Tangent:

Late last month, the Centers for Disease Control and Prevention decreased the recommended quarantine time from 14 days down to 10. "For most persons with Covid-19 illness, isolation and precautions can generally be discontinued 10 days after symptom onset," the CDC said. However, the JAMA study found that symptomatic patients did not become virus-free until around Day 19 or 20. (Asymptomatics were virus-free a little earlier, around Day 17.)

Number:

302: South Korea and the U.S. confirmed their first case of Covid-19 on the same day (January 20). The coronavirus was first detected in Florida on March 1. As of Thursday morning, there have been approximately 502,000 cases and 7,600 deaths in Florida (population 21 million). As of Thursday morning, there have been about 14,400 and 300 deaths in South Korea (population 52 million).

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