Researchers from Australia’s national science agency CSIRO have found that the COVID-19 coronavirus can survive on certain surfaces—such as banknotes and phone screens—for up to 28 days, roughly seven times longer than previous experiments suggested.
“These findings demonstrate SARS-CoV-2 can remain infectious for significantly longer time periods than generally considered possible. These results could be used to inform improved risk mitigation procedures to prevent the fomite spread of COVID-19,” the researchers wrote in their conclusion, published last week in Virology Journal. (A fomite is an inanimate object contaminated by an infectious agent.)
The experiment—measuring the time it took for samples of the virus to become inactive when left on different surfaces—was conducted at three ambient temperatures: 20°C, 30°C and 40°C. The virus survived longest on smooth surfaces, such as glass and plastic.
On glass and polymer banknotes—the smooth, wax-like notes used in Australia and other countries— it took 6 days for 90% of the virus sample to become inactive at 20°C. Paper money was even more hospitable, with 90% of the virus sample expiring after 9.13 days at 20°C.
“While the precise role of surface transmission, the degree of surface contact and the amount of virus required for infection is yet to be determined, establishing how long this virus remains viable on surfaces is critical for developing risk mitigation strategies in high contact areas,” deputy director of the Australian Centre for Disease Preparedness Debbie Eagles said.
China began treating its banknotes back in February, in a bid to stem transmission from currency. Banks were ordered to sterilize notes using either heat or UV light and then store the notes for 14 days before releasing the money into circulation. The country is perhaps the best poised to forego cash, too, as roughly 60% of the world’s mobile payment users are in China.
CSIRO’s research also found that the virus survived longest at a lower temperature. Observational evidence already suggested this was the case. In China, active COVID-19 samples have been found on packets of frozen food imports—suggesting the virus has survived on the frigid surface for weeks during transport. New Zealand investigated the possibility that frozen food imports carried COVID-19 into the country, too.
But even though the virus can survive on surfaces for longer than previously thought, surfaces themselves pose a relatively low transmission risk. The virus can only infect a person if it enters their body, usually through the mouth. CSIRO also conducted the experiment in the dark, to eliminate the damaging effects of UV-light on the virus. In normal situations, where surfaces are exposed to the elements, the virus might not survive for quite so long.
What the research reaffirms, Eagles says, is the importance of adopting best practices when it comes to personal hygiene—such as washing your hands at regular intervals, and cleaning surfaces.