Coronavirus: Around 10 percent of new infections come from people without symptoms - study

The virus which causes COVID-19 skips from person-to-person much more quickly than other viruses, and can survive for days on plastic surfaces, still able to infect, new research has found.

Two new studies have shed light on just how SARS-CoV-2 became a pandemic, infecting hundreds of thousands of people in just a few months and killing more than 14,000. 

The first, published in the New England Journal of Medicine, looked at just how the virus lasts once someone's coughed or sneezed it out. 

They found on copper it lasted four hours, on cardboard 24 hours and up to three days on plastic and stainless steel surfaces.

In aerosol form - very tiny droplets - it was detectable in the air for three hours. But this doesn't mean it's airborne, like the highly contagious measles. The aerosol had to be created artificially. 

"Aerosols are typically very small in size while coughs produce typically larger particles which settle quickly, although there is a distribution of size range with some small particles being produced which are small enough to remain suspended for longer," said Prof William Keevil, professor of environmental healthcare at the University of Southampton.

An undated scanning electron microscope image shows SARS-CoV-2 (yellow), the virus that causes COVID-19, isolated from a patient in the US.
An undated scanning electron microscope image shows SARS-CoV-2 (yellow), the virus that causes COVID-19, isolated from a patient in the US. Photo credit: Getty

But its durability on surfaces we use every day, like plastic, means it's as important as ever to heed advice about washing your hands regularly and avoiding touching your face (the virus enters the body through the nose, mouth and eyes). 

"The advice remains not to get too close to possible cases and wash your hands regularly, especially after touching surfaces before touching your own face," said medical professor Paul Hunter of the University of East Anglia.

The second study, published in journal Emerging Infectious Diseases, looked at how quickly the virus spread across China in its first few weeks. They found the average time for an infected person to pass it on to someone else was only four days - about the same as the flu. In comparison, Ebola can take weeks before it starts spreading. 

Around 10 percent of the infections they tracked came from patients who weren't showing any symptoms. 

"This provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted," said author Lauren Ancel Meyers, a professor of integrative biology at UT Austin. "Asymptomatic transmission definitely makes containment more difficult."

The research was worked on by scientists from Hong Kong, the US, China and France.