This scanning electron microscope image shows SARS-CoV-2 (orange)—also known as 2019-nCoV, the virus that causes COVID-19—isolated from a patient in the U.S., emerging from the surface of cells (green) cultured in the lab. Image captured and colorized at NIAID's Rocky Mountain Laboratories (RML) in Hamilton, Montana. Credit: NIAID (from Flickr)
This is an evidence-based approach to summarize the virucidal effect of far UVC light on the viruses in general, and the novel coronavirus in particular - including those present in aerosols. All PubMed and DOI links embedded in the article. The PDF version of this article can be downloaded from Dr. Rajeev Chitguppi's Researchgate.
Application of ultraviolet (UV) light against airborne pathogens: Is it a recent phenomenon?
The airborne antimicrobial efficacy of ultraviolet (UV) light has been utilized as a direct approach to prevent the transmission of the airborne-mediated disease via inactivation of the corresponding airborne pathogens, since long (from 1930s).
We know that there are UVA, UVB, and UVC lights, out of which it is the UVC light that is being used for the germicidal action. What is the drawback of conventional UVC light?
Since the conventional UVC light poses a human health hazard (carcinogenic and cataractogenic), the use of germicidal UV light in public settings has been very limited.
Is there any evidence to show that far-UVC light is effective as well as safer compared to the conventional UVC?
Studies by Buonanno et al have demonstrated that the use of far-UVC light generated by filtered excimer lamps (wavelength range 207 to 222 nm) efficiently inactivates drug-resistant bacteria, without apparent harm to exposed mammalian skin.
The reason for the safety of far UVC lights is its strong absorbance in biological materials, because of which far UVC light does not have sufficient range to penetrate through even the outer layer (stratum corneum) of the human skin, nor the outer tear layer on the outer surface of the eye - neither of these contains living cells.
However, the smaller dimension of bacteria and viruses (micron or smaller) enables the far-UVC light to efficiently traverse and inactivate them.
Severe acute respiratory syndrome (SARS) is a life-threatening disease caused by a novel coronavirus termed SARS-CoV. Due to the severity of this disease, the World Health Organization (WHO) recommends that manipulation of active viral cultures of SARS-CoV be performed in containment laboratories at biosafety level 3 (BSL3). The virus was inactivated by ultraviolet light (UV) at 254 nm, heat treatment of 65 degrees C or greater, alkaline (pH > 12) or acidic (pH < 3) conditions, formalin and glutaraldehyde treatments. We describe the kinetics of these efficient viral inactivation methods, which will allow research with SARS-CoV containing materials, that are rendered non-infectious, to be conducted at reduced safety levels.
"Our experiments showed that UVC light, heat, formalin, glutaraldehyde, and extremes of pH, were able to inactivate SARS-CoV."
Background and objective: Severe acute respiratory distress syndrome coronavirus-2 (SARS-CoV-2), the causative agent of coronavirus disease 2019 (COVID-19), is a member of the coronavirus family. Coronavirus infections in humans are typically associated with respiratory illnesses, however, viral RNA has been isolated in serum from infected patients. Coronaviruses have been identified as a potential low-risk threat to blood safety. The Mirasol Pathogen Reduction Technology (PRT) System utilizes riboflavin and ultraviolet (UV) light to render bloodborne pathogens noninfectious while maintaining blood product quality. Here we report on the efficacy of riboflavin and UV light against the pandemic virus SARS-CoV-2 when tested in both plasma and platelets units.
Materials and methods: Stock SARS-CoV-2 was grown in Vero cells and inoculated into either plasma or platelet units. Those units were then treated with riboflavin and UV light. The infectious titers of SARS-CoV-2 were determined by plaque assay using Vero cells. A total of five (n=5) plasma and three (n=3) platelet products were evaluated in this study.
Results: In both experiments, the measured titer of SARS-CoV-2 was below the limit of detection following treatment with riboflavin and UV light. The mean log reductions in the viral titers were ≥3.40 and ≥4.53 for the plasma units and platelet units, respectively.
Conclusion: Riboflavin and UV light effectively reduced the titer of SARS-CoV-2 in both plasma and platelet products to below the limit of detection in tissue culture. The data suggest that the process would be effective in reducing the theoretical risk of transfusion-transmitted SARS-CoV-2.
Coming to the main issue: Viruses in aerosols. Are there any studies that show the effect of far UVC light against the viruses present in the aerosols?
For the first time, the efficacy of far-UVC 222-nm light was tested for inactivating airborne viruses carried by aerosols – on the spread of influenza A via aerosol transmission, in order to provide a potentially safe alternative to conventional 254-nm germicidal lamps to inactivate airborne microbes.
Airborne-mediated microbial diseases such as influenza and tuberculosis represent major public health challenges. A direct approach to prevent airborne transmission is inactivation of airborne pathogens, and the airborne antimicrobial potential of UVC ultraviolet light has long been established; however, its widespread use in public settings is limited because conventional UVC light sources are both carcinogenic and cataractogenic. By contrast, we have previously shown that far-UVC light (207-222 nm) efficiently inactivates bacteria without harm to exposed mammalian skin. This is because, due to its strong absorbance in biological materials, far-UVC light cannot penetrate even the outer (non-living) layers of human skin or eye; however, because bacteria and viruses are of a micrometre or smaller dimensions, far-UVC can penetrate and inactivate them. We show for the first time that far-UVC efficiently inactivates airborne aerosolized viruses, with a very low dose of 2 mJ/cm2 of 222-nm light inactivating >95% of aerosolized H1N1 influenza virus. Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.
"Our results indicate that far-UVC light is a powerful and inexpensive approachforprevention and reduction of airborne viral infections without the human health hazards inherent with conventional germicidal UVC lamps. If these results are confirmed in other scenarios, it follows that the use of overhead very low-level far-UVC light in public locations may represent a safe and efficient methodology for limiting the transmission and spread of airborne-mediated microbial diseases. Public locations such as hospitals, doctors’ offices, schools, airports and airplanes might be considered here. This approach may help limit seasonal influenza epidemics, the transmission of tuberculosis, as well as major pandemics."
Connecting the three dots: (1) far UVC light (2) human coronaviruses (3) aerosols
and coming to the most critical issue:Effect of far UVC light against human coronaviruses in aerosols? Are there any studies that show the effect of far UVC light against the human coronaviruses present in the aerosols?
A direct approach to limit airborne transmission of pathogens is to inactivate them within a short time of their production. Germicidal ultraviolet light (UV), typically at 254 nm, is effective in this context, but it is a health hazard to the skin and eyes. By contrast, far-UVC light (207-222 nm) efficiently kills pathogens without harm to exposed human cells or tissues.
We had previously demonstrated that 222-nm UV light efficiently kills airborne influenza virus (H1N1); here we extend the far-UVC studies to explore efficacy against human coronaviruses from subgroups alpha (HCoV-229E) and beta (HCoV-OC43).
We found that low doses of, respectively 1.7 and 1.2 mJ/cm2 inactivated 99.9% of aerosolized alpha coronavirus 229E and beta coronavirus OC43.
Based on these results for the beta HCoV-OC43 coronavirus, continuous far-UVC exposure in public locations at the currently recommended exposure limit (3 mJ/cm2/hour) would result in 99.9% viral inactivation in ~ 25 minutes.
Increasing the far- UVC intensity by, say, a factor of 2 would halve these disinfection times, while still maintaining safety.
As all human coronaviruses have similar genomic size, a key determinant of radiation sensitivity, it is realistic to expect that far-UVC light will show comparable inactivation efficiency against other human coronaviruses, including SARS-CoV-2.
This is an animated presentation showing how far-UVC light works to prevent the airborne spread of coronavirus & influenza virus:
TED talk: In a talk from the frontiers of science, radiation scientist David Brenner shares his work studying a potentially life-saving weapon: a wavelength of ultraviolet light known as far-UVC, which can kill superbugs safely, without penetrating our skin.
For more experimental evidence by David J Brenner and his team at Columbia University Medical Center, please click on the links below to view the current publications on Far UVC:
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