When airborne droplets laden with COVID-19 were exposed to a specific wavelength of ultraviolet light, more than 99.9 percent of the viral particles were killed, according to new research at the Columbia University Irving Medical Center. The researchers, led by scientist David Brenner, recently published a paper discussing the effect potentially human-safe far-UVC rays have on the coronavirus family. “Based on our results,” writes Brenner, “continuous airborne disinfection with far-UVC light at the current regulatory limit could greatly reduce the level of airborne virus in indoor environments occupied by people.”
If this ultraviolet light is safe for human exposure, it could add another low-cost method of virus mitigation to our toolkit. How would such technology be applied to reduce the spread of COVID-19? Brenner continues: “Because it’s [likely] safe to use in occupied spaces like hospitals, buses, planes, trains, train stations, schools, restaurants, offices, theaters, gyms, and anywhere that people gather indoors, far-UVC light could be used in combination with other measures, like wearing face masks and washing hands, to limit the transmission of SARS-CoV-2 and other viruses.”
Unfortunately, there are caveats and unknowns. For instance, to kill 99 percent of the virus, it needs to be exposed to the light for at least 25 minutes. However, killing 90 percent of the virus takes eight minutes. The trouble is in finishing off the last ten percent of the virus.
But how long would such lights need to make a coronavirus-laden sneeze impotent? After all, while the virus can be transmitted on surfaces, the more dangerous pathway are the airborne and newly emitted viral droplets. And the time frame of when the virus is killed is important, not just the end percentage.
There are also some lingering concerns that human exposure to far-UVC 222nm may not be entirely safe. “The Sterilray disinfectant source (222 nm) conventionally used to sterilize equipment and work surfaces was assessed for tolerability in human skin found potential dangers of exposure to 222 nm wavelengths when looking to see if UV lights could be used as an alternative to antiseptic use in medical facilities,” according to a 2015 study. It should be noted that this study was specifically looking at neutralizing bacteria on the hands of the test subjects, not viruses. Dr. Brenner and his team have yet to address the 2015 study’s findings, so it is unknown what the ultraviolet requirements between bacterial and viral destruction might be and what that difference means for public health.
This, then, is potentially good news tempered by the relatively slow time to kill and the possible medical side effects. To hear more about Dr. Brenner’s research, the challenges it faces, and the potential impact this technology could have, please see this TED talk interview.