Suthe brightness can be a Achilles’ heel of SARS-CoV-2. It has been known for some time that the coronavirus that causes COVID-19 is quickly destroyed on a surface immersed in simulated sunlight, but a team of scientists now argues that the virus may be even more susceptible to ultraviolet radiation than previously estimated.
In July 2020 an important study found that simulated sunlight “quickly deactivates SARS-CoV-2” on surfaces. By his estimates, 90 percent of the SARS-CoV-2 virus was inactivated every 6.8 minutes in the simulated saliva when exposed to simulated sunlight representative of a clear summer day at sea level. In the following month, another study produced a theoretical model that described the solar inactivation of SARS-CoV-2.
However, there is some discrepancy between these results, according to a team of researchers from UC Santa Barbara, Oregon State University, University of Manchester and ETH Zurich writing at the Jouend of infectious diseases. They explain that the laboratory experiments show the inactivation of sunlight several times faster than predicted by the theory. In fact, viruses were inactivated eight times faster in experiments than would have been predicted by the theory.
To explain this gap, they argue that we need to look beyond ultraviolet B (UVB), the high-energy ultraviolet light associated with skin burn, and start paying more attention to ultraviolet A (UVA), the lowest energy component of light skin associated with aging skin.
“The theory assumes that inactivation works by causing UV-B to reach the virus’s RNA, damaging it”, Paolo Luzzatto-Fegiz, lead author of the Department of Mechanical Engineering at the University of California at Santa Barbara, said in a demonstration.
“People think that UV-A does not have much effect, but it may be interacting with some of the molecules in the medium,” added Luzzatto-Fegiz.
This is all just conjecture for now. The researchers did not perform any modeling or experiment on their own, but simply highlighted the peculiar discrepancy between data and theory.
“So, scientists still don’t know what’s going on,” added Luzzatto-Fegiz; “Our analysis points to the need for additional experiments to separately test the effects of specific wavelengths and composition of the medium.”
If they are in the money, it can be promising news. Some hospitals and other high-risk environments disinfect their air using the power of UVC, which has even higher energy than UVB. Although, this wavelength is largely absorbed by the Earth’s ozone layer and does not reach the surface, which means that it must be created artificially.
“UV-C is great for hospitals,” adds co-author Julie McMurry. “But in other environments – for example, kitchens or subways – the UVC would interact with the particles to produce harmful ozone.”
On the other hand, UVA is safe and easy to generate with inexpensive LED lamps that are often more powerful than natural sunlight. If UVA is really the missing piece in the puzzle, it could easily be implemented in air filtration systems and disinfection methods to slow the spread of COVID-19 in high-risk spaces.