By Rebecca Lynch

With the arrival of the new coronavirus, SARS-CoV-2, research is growing in the area of rapid, safe limitation of airborne and surface viral transmissions. One usage is a type of ultraviolet (UV) light device for disinfecting surfaces and objects, such as the cabinets used by hospital staff upon arrival at work to sanitize their mobile phones and small personal items.  

UV disinfecting technology also has potential to safely disinfect air in the presence of humans, as noted in a recent article in Nature Research’s Scientific Reports, which discusses the effectiveness of “far-UVC” light (222 nm) as an inactivator of airborne human coronaviruses.  

UV light has been known to be effective against bacteria and viruses, but the commonly-used wavelength of 254 nm is a health hazard to skin and eyes; whereas, far-UVC light (207 nm – 222 nm) kills pathogens effectively but doesn’t appear to harm exposed mammalian skin. The reasoning is based on the limited penetration of the lower-wavelength light in biological samples such as the stratum corneum, compared to that of 254 nm light. 

The Scientific Reports authors previously showed the effectiveness of 222 nm light against airborne influenza virus. Using the same krypton-chlorine excimer lamp from the 222-nm studies and adding a bandpass filter, they’ve extended their studies to two airborne human coronaviruses (HCoV-229E and beta HCoV-OC43). In both cases they showed greater than 99% virus inactivation with low light doses under 1.7 mJ/cm2 with no evidence of cytotoxicity to exposed mammalian skin. Because all human coronaviruses have similar genomic sizes, the authors expect similar efficacy against SARS-CoV-2. They also note that far-UVC exposure at the current regulatory limit of ~3 mJ/cm2/hour would result in greater than 90% viral inactivation in about 8 minutes, with 99.9% levels achieved in about 25 minutes. 

BioSpace also reports commercial development of far-UVC devices by Boston University’s National Emerging Infectious Diseases Laboratories.  Their work confirms the expected efficacy against SARS-CoV-2, in their case using a 5 mJ/cm2 dose of UVC and eradicating 99% of the virus in 6 seconds. The team notes that while further studies are needed, but no viruses or bacteria tested during the past 40 years have shown resistance to UVC light. 

FDA offers a comprehensive resource page on UVC disinfection and coronavirus.   UVC lamps are electronic products that emit radiation; these devices (both medical and non-medical) are currently regulated through the Electronic Product Radiation Control Provisions. If the lamps are classified as medical devices they are also regulated as such. 

Image: Adapted from UV Resources – https://uvresources.com/