More than 99.9% of seasonal coronaviruses present in airborne droplets were killed when exposed to a particular wavelength of ultraviolet light that is safe to use around humans, a study at Columbia University Irving Medical Centre has found. "Based on our results, 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," says the study's lead author Dr David Brenner, Higgins professor of radiation biophysics at Columbia University Vagelos College of Physicians and Surgeons and director of the Centre for Radiological Research at Columbia University Irving Medical Centre.
Conventional germicidal UVC light (254 nm wavelength) can be used to disinfect unoccupied spaces such as empty hospital rooms or empty subway cars, but direct exposure to these conventional UV lamps is not possible in occupied public spaces, as this could be a health hazard.
To continuously and safely disinfect occupied indoor areas, researchers at Columbia University Irving Medical Centre have been investigating far-UVC light (222 nm wavelength). Far-UVC light cannot penetrate the tear layer of the eye or the outer dead-cell layer of skin so it cannot reach or damage living cells in the body.
The researchers had previously shown that far-UVC light can safely kill airborne influenza viruses.
The new paper extends their research to seasonal coronaviruses, which are structurally similar to the SARS-CoV-2 virus that causes COVID-19.
In the study, the researchers used a misting device to aerosolise two common coronaviruses. The aerosols containing coronavirus were then flowed through the air in front of a far-UVC lamp. After exposure to far-UVC light, the researchers tested to see how many of the viruses were still alive.
The researchers found that more than 99.9% of the exposed virus had been killed by a very low exposure to far-UVC light.
Based on their results, the researchers estimate that continuous exposure to far-UVC light at the current regulatory limit would kill 90% of airborne viruses in about 8 minutes, 95% in about 11 minutes, 99% in about 16 minutes, and 99.9% in about 25 minutes.
The sensitivity of the coronaviruses to far-UVC light suggests that it may be feasible and safe to use overhead far-UVC lamps in occupied indoor public places to markedly reduce the risk of person-to-person transmission of coronaviruses, as well as other viruses such as influenza.
In a separate ongoing study, the researchers are testing the efficacy of far-UVC light against airborne SARS-CoV-2. Preliminary data suggest that far-UVC light is just as effective at killing SARS-CoV-2.
"Far-UVC light doesn't really discriminate between coronavirus types, so we expected that it would kill SARS-CoV-2 in just the same way," Brenner says. "Since SARS-CoV-2 is largely spread via droplets and aerosols that are coughed and sneezed into the air it's important to have a tool that can safely inactivate the virus while it's in the air, particularly while people are around."
Brenner continues, "Because it's safe to use in occupied spaces like hospitals, buses, planes, trains, train stations, schools, restaurants, offices, theatres, 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."
The study was funded by the Shostack Foundation and the NIH (grant R42-AI125006-03).
A direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production. Germicidal ultraviolet light, typically at 254 nm, is effective in this context but, used directly, can be a health hazard to skin and eyes. By contrast, far-UVC light (207–222 nm) efficiently kills pathogens potentially without harm to exposed human tissues. We previously demonstrated that 222-nm far-UVC light efficiently kills airborne influenza virus and we extend those studies to explore far-UVC efficacy against airborne human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Low doses of 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized coronavirus 229E and OC43, respectively. As all human coronaviruses have similar genomic sizes, far-UVC light would be expected to show similar inactivation efficiency against other human coronaviruses including SARS-CoV-2. Based on the beta-HCoV-OC43 results, continuous far-UVC exposure in occupied public locations at the current regulatory exposure limit (~3 mJ/cm2/hour) would result in ~90% viral inactivation in ~8 minutes, 95% in ~11 minutes, 99% in ~16 minutes and 99.9% inactivation in ~25 minutes. Thus while staying within current regulatory dose limits, low-dose-rate far-UVC exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses in occupied public locations.
Manuela Buonanno, David Welch, Igor Shuryak, David J Brenner
Columbia University Irving Medical Centre material
Scientific Reports abstract