The study also found that the virus survived longer at lower temperatures and tended to last longer on non-porous or smooth surfaces such as glass and stainless steel rather than porous or rough surfaces such as cotton.
“Establishing how long the virus really remains viable on surfaces enables us to more accurately predict and mitigate its spread and do a better job of protecting our people,” Larry Marshall, the CEO of Australia’s national science agency CSIRO, said in a statement.
Around a room temperature of 68 degrees Fahrenheit, the coronavirus could last for 28 days on smooth surfaces. At higher temperatures, the survival time decreased as the temperature increased, and on cotton, the virus wasn’t detectable after 14 days.
However, the study was conducted in the dark to remove the effect of UV light, which can inactivate the virus. That means the lab conditions may not match the real world. The items were left undisturbed as well, but phone screens and banknotes are often moved around, which could wipe off the virus.
“What we’re seeing empirically, clinically, with contact tracing, is that COVID is not spreading heavily through touch,” Colin Furness, an infection control epidemiologist at the University of Toronto, told CTV News.
“It is possible to contract the virus through surfaces,” he said. “But it’s not happening very often.”
In addition, the study tested how long the virus lasts on surfaces but not how long the virus particles are actually infectious. Influenza A, for instance, has been found to survive on surfaces for 17 days, but a virus begins to degrade once it leaves a host’s body.
“How long [a virus] can survive and remain infectious depends on the type of virus, quantity, the surface, environmental conditions and how it’s deposited -- for example, touch versus droplets emitted by coughing,” Trevor Drew, director of the Australian Centre for Disease Preparedness, said in the statement.
Other scientists have said the study could cause “unnecessary fear” because the virus mostly spreads among humans through respiratory droplets from coughing and sneezing rather than dirty surfaces, Ron Eccles, former director of the Common Cold Centre at Cardiff University, told BBC.
“Fresh mucus is a hostile environment for viruses as it contains lots of white cells that produce enzymes to destroy viruses and can also contain antibodies and other chemicals to neutralize viruses,” he said. “In my opinion, infectious viruses will only persist for hours in mucus on surfaces rather than days.”
At 68 degrees Fahrenheit, the half-life -- or the time required to eliminate half of the initial amount of the virus -- on paper money was about 2.74 days. After 9 days, 90% of the virus was gone.
On cotton, the half-life was 1.68 days, and 90% of the virus was gone after about 5.5 days.
The study didn’t measure samples at less than 68 degrees. Based on the rate of virus decomposition at higher temperatures, though, the researchers suggested that the coronavirus could last longer in colder temperatures.
“This data could therefore provide a reasonable explanation for the outbreaks of COVID-19 surrounding meat processing and cold storage facilities,” they wrote.
Other studies have suggested that cold and damp environments, close working conditions, and a noisy work environment in meat processing plants could cause people to shout and spread respiratory droplets, the BBC reported.
Despite the limitations, the study may pose a reminder for frequent handwashing and regular disinfection of surfaces, especially during colder months.
“I wonder whether we’re going to see that COVID does spread more by touch in the winter,” Furness told CTV News. “I can't say that it does, but it’s entirely possible that it will.”