Study: Ultraviolet-C light kills coronavirus on N95 masks

Ultraviolet-C light kills coronavirus on N95 respirator masks, effectively decontaminating them so they can safely be reused, dermatology researchers at Henry Ford Health System and the University of Michigan announced Tuesday.
A shortage of the medical-grade masks early in the COVID-19 pandemic drove the health systems to collaborate on a project to test whether a high dose of UV-C light – used to treat some skin conditions like vitiligo and psoraisis –
would kill virus particles but still preserve the integrity of the masks.


Five types of N95s were tested during the study at U-M’s SARS-CoV-2 research lab in Ann Arbor. They were contaminated with four drops of the virus from the federal government’s Biodefense and Emergency Infections Research Resources Repository. The virus droplets were placed in four areas of each mask: the nosepiece, apex, chin and strap.
Scientists discovered that masks could be decontaminated in less than two minutes using the UV-C light. The process was most effective on different parts of the five models they tested – the facepieces of the 3M 1860 mask and the Moldex 1511 as well as the straps of the 3M 8210 and the Moldex 1511.


“Our findings reveal a practical, and viable option should hospitals encounter shortages of N95s in the future,” said Dr. David Ozog, chair of Henry Ford’s Department of Dermatology in Detroit and the lead author of a study published earlier this month in the International Journal of Infectious Diseases, in a statement.
“Using UV-C has been shown to be effective in killing other coronaviruses and the flu virus,” he said. “We were able to replicate that sterilization effectiveness with COVID-19.”
Although the study shows medical-grade face masks can be decontaminated using light, Ozog stressed that it should only used when there are severe shortages of N95s. Soiled masks should be thrown away rather than decontaminated. Researchers also recommended wiping the straps of the masks with ethanol before treating them with UV-C light as an additional safety precaution.
Some mask straps showed signs of degrading after being exposed to the light, and researchers said all masks that have been decontaminated in this way should be fit tested before use.


“When Dr. Ozog approached us about helping to demonstrate the effectiveness of their UV sterilization procedure with live SARS-CoV-2 virus, we immediately agreed and understood that we could provide some confidence to their health care workers that this procedure was effective,” said Jonathan Sexton, Ph.D., director of the U-M Center for Drug Repurposing and a study co-author, in a statement.
When the crush of COVID-19 cases hit southeastern Michigan in March and early April, it revealed a weak link in the medical supply chain as hospital systems were overwhelmed with patients and discovered that they didn’t have enough personal protective equipment, including N95 masks.


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Many of them, including Henry Ford, tried to decontaminate N95 masks so they could be re-used.
“The beginning of the pandemic was physically and mentally overwhelming for everyone. We desperately wanted to help our front-line workers, who were crushed with COVID-19 cases at Henry Ford,” Ozog said.
Although UV-C light has been shown to be an effective way to disinfect masks contaminated with coronavirus, researchers warned that it should only be used when there are supply shortages. And soiled masks should never be decontaminated and reused.
Discarding a contaminated disposable N95 after a single use is “still ideal,” said Dr. Angela Torres, a Henry Ford dermatology fellow in a statement.