A new Australian study analyzing the survival rate of SARS-CoV-2 on a variety of surfaces has found that the virus can survive up to 28 days on glass, stainless steel or even paper money. However, experts urge caution in interpreting these results, as they do not translate into conditions that affect the spread of COVID-19 in the real world.
The new study, from a team from the Australian Centers for Disease Control and Prevention (ACDP), focused on the effects of temperature on the life of SARS-CoV-2, the virus that causes COVID-19. In order to eliminate other variables that affect the survival of the virus, the study was conducted under tightly controlled laboratory conditions.
The researchers suspended the virus in artificial mucus to mimic the composition of the body’s secretions. Experiments are conducted in the dark to eliminate the destructive effects of ultraviolet light on the virus. Moreover, in all tests, the ambient humidity is permanently locked at 50%.
The survival rate of the virus is then tested on several different surfaces at three different temperatures, at 20 degrees C/30 degrees C/40 degrees C. The core results of the study show that viruses do survive longer at lower temperatures. It also survives longer on holeless and smooth surfaces such as glass and stainless steel.
“At 20 degrees Celsius (about room temperature), we found that the virus was very powerful and survived on smooth surfaces for 28 days, such as glass and banknotes on mobile phone screens,” explained Debbie Eagles, author of the new study and deputy director of ACDP.
These findings are robust and of course of scientific value, increasing understanding of the new coronavirus, but the general public’s interpretation of the media coverage of the study, in many cases focusing only on the sensational findings that the virus can survive a month on banknotes and mobile phone screens, without any restrictions on the spread of the real world.
Hassan Valley, an epidemiologist at La Thyb University, stressed that applying the findings to real-world public health conditions is limited. “Under the conditions of this study, viruses can survive longer than previously thought, and this condition is not universally applicable to the real world, which is of limited value for understanding the relative importance of the surface of exposure as a route of COVID-19 transmission.” Valley explains.
Timothy Newsome, a virologist from the University of Sydney, supports Valley’s concerns about the value of research affecting an individual’s own perception of risk. He argues that studying the persistence of viruses in isolation does not explain many real-world variables that affect the risk of transmission.
Newsome notes that “infectious doses, the effects of saliva and mucus on longevity, social behavior, and real environmental stress factors, such as sunlight,” are all relevant when accounting for the spread of the virus under real-world conditions.
However, Newsome does believe that the new study may have some usefulness, especially in defining what is possible. Understanding possible, though not common, transmission routes can provide information for more effective and extensive public health recommendations.
“It has been found that in some, albeit man-made, situations (in the dark), viruses live longer than previously thought, providing information for contact tracing and risk management,” Newsome said. “For example, surface propagation cannot be ruled out when the transmission interval between individuals is several days, especially in cold environments where there is a lack of sunlight. Defining the persistence of a virus can also provide information for the defaced program. “
The Australian team behind the new study makes it clear that a staggering 28 days of survival is not necessarily a realistic indicator of how well the virus is performing in the real world. However, Eagles did confirm the value of the discovery, saying it was critical for the authorities to develop risk mitigation strategies.
“While the exact role of surface transmission, the extent of surface exposure, and the amount of virus required for infection have yet to be determined, establishing the survival time of the virus on the surface is critical to developing risk mitigation strategies in high-contact areas.” Eagles said.
Some experts believe the new study has limitations and the results are almost irrelevant. Ron Eccles, from Cardiff University, told the BBC he questioned the mucus solution used in the study. He points out that human mucus is a complex combination of compounds and says the virus is unlikely to last on the surface for several days.
“The virus is transmitted on the surface by coughing, sneezing, and mucus in dirty fingers, and this study does not use fresh human mucus as a vector for transmitting the virus,” Eccles said. “Fresh mucus is a hostile environment for viruses because it contains large amounts of white blood cells, which produce enzymes that destroy the virus and can also contain antibodies and other chemicals to completely damage the virus.”
Faheem Younus, an infectious disease expert at the University of Maryland, called the new study “nonsense” on Twitter. He said the artificial laboratory conditions used in the experiment simply could not be extended to the real world, adding that banknotes and mobile phones were not a risk to COVID-19. He even joked that if the people concerned were still afraid, they should give him money and mobile phones.
These concerns about the new findings are based on the growing belief convinced that the vast majority of COVID-19 cases are due to respiratory transmission rather than surface transmission. In the nearly a year since the pandemic, cluster case studies have shown that surface transmission of the virus is rare.
Monica Gandhi, from the University of California, San Francisco, points out that this shift from fear of surface propagation to more aerosol forms is one of the key things we’ve learned in the past six months. “At the beginning of the pandemic, there was a lot of fear of surface transmission, ” Gandhi said in a recent interview. “We now know that the root cause of transmission does not come from touching the surface and touching the eyes. It comes from people close to spraying the virus from their noses and mouths, and in most cases they don’t know they’re doing it. “
So while the new study provides valuable new insights into how SARS-CoV-2 survives on the surface under certain environmental conditions, it certainly doesn’t mean that virus particles that “sleep” for weeks on paper money or mobile phones are at high risk of transmission.
The new study was published in the journal Virology.