Newswise — The emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and its subsequent variants on a global scale has highlighted the crucial requirement for reliable disinfection technologies to combat dangerous pathogens. Although vaccines provide a level of protection, their effectiveness against future variants remains uncertain. Consequently, it becomes imperative to implement supplementary strategies, particularly during the pre-vaccine phase, to safeguard against potential threats.
In recent times, UV irradiation has emerged as a secure, effective, and convenient method to deactivate and eradicate disease-causing microorganisms. Among the various UV wavelengths, the range of 200-235 nm, known as far-UVC, has garnered increasing interest as a promising disinfection wavelength. While far-UVC has been demonstrated to be harmless to mammalian cells due to the strong absorption effect of the stratum corneum layer, its safety on mammalian cells is not yet fully established. Concerns have been raised about potential damage to skin cells when exposed to high levels of far-UVC light. Moreover, existing study data shows significant inconsistencies, possibly due to variations in the strains of SARS-CoV-2 used and differences in experimental conditions, such as the spectrum of light sources utilized.
To address these uncertainties, Professor Takahiro Matsumoto and his team from the Graduate School of Design and Architecture at Nagoya City University conducted systematic experiments using varying UV wavelengths while keeping other experimental conditions constant. The dedicated group of scientists involved in this research includes Professor Makoto Tomita from Shizuoka University, Professor Tadao Hasegawa from Nagoya City University, Professor Yasuhito Tanaka from Kumamoto University, and others. Their comprehensive study was published online on 15th June 2023 in the esteemed journal Scientific Reports.
The team conducted a series of experiments to investigate the interaction of UV rays with two omicron variants of the coronavirus. Initially, they extracted the omicron BA.2 and BA.5 variants of SARS-CoV-2 from infected cells (VeroE6/TMPRSS2). Subsequently, these isolated variants were exposed to UV irradiation across a range of wavelengths, spanning from 200 to 260 nm. To assess the impact of the UV treatment, they applied varying doses of UV irradiation, ranging from 0 to 18 mJ/cm2, for each wavelength.
To gauge the effectiveness of the UV treatment, the team employed two methods, namely TCID50 (tissue culture infectious dose) and qPCR (quantitative polymerase chain reaction), to calculate the inactivation rate constant. These analyses provided valuable insights into the efficiency of the UV irradiation treatment against the omicron variants of SARS-CoV-2.
The study revealed that both omicron BA.2 and BA.5 variants exhibit nearly identical UV inactivation properties. While the highest inactivation rates were observed at 260 nm, the rates obtained with 220 nm light were comparable to those achieved with the former. These results underscore the promising potential of far-UVC light as a safe germicidal option. Professor Matsumoto concludes, "The similar inactivation efficacy between 220 nm and 260 nm light indicates that far-UVC light could offer a viable and safe approach to mitigate airborne virus transmission."
Furthermore, the research found that the UV inactivation rate constants measured in a liquid suspension were approximately 10 times lower than those previously observed in an aerosol state. This suggests that the Mie scattering effect might play a role in enhancing UV irradiance within aerosol droplets, leading to more efficient inactivation of the virus in the aerosol form.
Moreover, the study employed the bacterium E. coli as a reference to discern and comprehend the distinctions in inactivation and genome damage when compared to the SARS-CoV-2 omicron variants. Remarkably, the research revealed that both SARS-CoV-2 and E. coli displayed similar sensitivities to UV light above 240 nm, suggesting that UV-induced inactivation primarily targets their genetic material (DNA or RNA). However, below 240 nm, significant variations were observed, likely attributable to the differences in the thickness of the protein layer enveloping their genetic material.
Furthermore, the spectral sensitivities derived from both TCID50 assays and qPCR assays displayed a correlation between the two methods, strengthening the reliability and consistency of their findings.
This study offers significant and valuable insights into the UV vulnerability of SARS-CoV-2 omicron variants. The similarity in inactivation effectiveness between 220 nm and 260 nm light, particularly when dealing with aerosols, indicates the promising application of far-UVC light in effectively preventing airborne virus transmission while ensuring safety and feasibility. These findings are expected to pave the way for the development of secure and practical ultraviolet sterilization technologies in the near future.
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