UV Inactivation of SARS-CoV-2 across the UVC Spectrum: KrCl* Excimer, Mercury-Vapor, and Light-Emitting-Diode (LED) Sources

Abstract

Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmission during the ongoing COVID-19 global pandemic and in the future. UV devices emitting UVC irradiation (200 to 280 nm) have proven to be effective for virus disinfection, but limited information is available for SARS-CoV-2 due to the safety requirements of testing, which is limited to biosafety level 3 (BSL3) laboratories. In this study, inactivation of SARS-CoV-2 in thin-film buffered aqueous solution (pH 7.4) was determined across UVC irradiation wavelengths of 222 to 282 nm from krypton chloride (KrCl*) excimers, a low-pressure mercury-vapor lamp, and two UVC light-emitting diodes. Our results show that all tested UVC devices can effectively inactivate SARS-CoV-2, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate). The inactivation rate constants of SARS-CoV-2 across wavelengths are similar to those for murine hepatitis virus (MHV) from our previous investigation, suggesting that MHV can serve as a reliable surrogate of SARS-CoV-2 with a lower BSL requirement (BSL2) during UV disinfection tests. This study provides fundamental information on UVC's action on SARS-CoV-2 and guidance for achieving reliable disinfection performance with UVC devices. IMPORTANCE UV light is an effective tool to help stem the spread of respiratory viruses and protect public health in commercial, public, transportation, and health care settings. For effective use of UV, there is a need to determine the efficiency of different UV wavelengths in killing pathogens, specifically SARS-CoV-2, to support efforts to control the ongoing COVID-19 global pandemic and future coronavirus-caused respiratory virus pandemics. We found that SARS-CoV-2 can be inactivated effectively using a broad range of UVC wavelengths, and 222 nm provided the best disinfection performance. Interestingly, 222-nm irradiation has been found to be safe for human exposure up to thresholds that are beyond those effective for inactivating viruses. Therefore, applying UV light from KrCl* excimers in public spaces can effectively help reduce viral aerosol or surface-based transmissions.

Keywords: COVID-19; MHV; UV disinfection; bacteriophage Phi6; far UVC; human coronavirus 229E; murine hepatitis virus; surrogate.

FIG 1

Schematic diagram of bench-scale collimated beam apparatus (A) and relative lamp emission (RLE) for the UV devices used in this investigation, absorbance of samples used in UV exposure tests, and normalized absorbance (normalized to maximum value at 200 nm) of nucleic acid (DNA/RNA) and protein (B). The nucleic acid and protein absorbance data were reproduced from Ma et al. (22).

FIG 2

Dose response of SARS-CoV-2 to UV irradiation from all tested UVC devices. Dashed lines represent linear regression results computed from experimental data. The k values (mean ± standard error in cm²/mJ) and adjusted R² values are listed. Open symbols represent samples with infectivity equal to or less than the detection limits. Solid symbols with a black edge represent two samples overlapping in the plot with the same UV dose response. Primary emission wavelengths for UVC devices are listed in each panel.

FIG 3

UV inactivation rate constants of SARS-CoV-2, two coronaviruses (HCoV 229E and MHV), and enveloped bacteriophage Phi6 for all tested UVC devices. The mean inactivation rate values are labeled. The values for Phi6, HCoV 229E, and MHV were published by Ma et al. (22). Asterisk brackets represent two inactivation rate values that were not statistically significantly different at the 95% confidence level (P > 0.05).