Health & Wellness

Symptom-Free Is No Guarantee

People with no symptoms can still spread COVID-19


Photo: iStock/wildpixel.


A number of recent studies may help explain why COVID-19 has been spreading so rapidly around the world.

Published by the US Centers for Disease Control and Prevention (CDC), a study by researchers in Singapore found evidence that the novel coronavirus that causes COVID-19 is often spread by those without any symptoms who carry the virus without knowing it.

About 10% per cent of all new cases may have caught the disease from those who are asymptomatic, researchers estimated. A previous study from China published in late March found the same thing, estimating that 12% of all cases could stem from such contact.

The Singapore study found that transmission happened one to three days before the “source” came down with the illness himself or herself. With this in mind, the study recommends that health officials conducting contact tracing look at who carriers came in contact with before becoming symptomatic.

“These findings suggest that to control the pandemic it might not be enough for only persons with symptoms to limit their contact with others because persons without symptoms might transmit infection,” the researchers wrote.

In a US radio interview in late March, CDC director Dr. Robert Redfield said that as many as 25% of those who test positive for COVID-19 are asymptomatic. However, study results from Iceland released a few days later indicated that the number may be much higher: while fewer than 1% of Icelanders tested for the virus tested positive, roughly 50% of those patients said they had no symptoms.

Another study, published in the New England Journal of Medicine, suggests that COVID-19 is much more contagious than SARS—the severe acute respiratory syndrome that came out of China in 2002—because SARS spread only among those showing symptoms.