Susceptibility of SARS-CoV-2 to UV Irradiation

The following is a summary of an article published August 4, 2020, by the American Journal of Infection Control.

In the journal, the authors’ main finding is that SARS-COV-2 is extremely susceptible to ultraviolet radiation. The novel coronavirus (SARS-CoV-2) triggering a severe respiratory condition was first identified in the Hubei province of China, in December 2019. Soon the coronavirus, or otherwise termed Covid-19, became a global health burden and caused heavy socio-economic disruption. Millions of cases have already been reported worldwide. As of now, prevention of the transmission of the virus is the only option to stop it. Especially, preventing the virus from transmitting within hospitals and other institutions is extremely necessary. Therefore, the authors investigated the susceptibility of high tier viral stocks of SARS-COV-2 

to combined or separate UVA and/or UV-C  irradiation. 

The authors isolated SARS-COV-2 from a nasopharyngeal swab. The sample was taken from a patient who was suffering from Covid-19 disease and was hospitalized at the Department of Infectious Diseases of the University Hospital Essen. The Virocult® medium (swab was taken using it) was incubated on Vero E6, cultured in DMEM containing 10% (v/v) fetal calf serum, and was supplemented with Penicillin (100 IU/ml), Streptomycin (100 µg/ml), Ciprofloxacin (10 µg/ml) and Amphotericin B (2.5 µg/ml). 

The supernatant was harvested after five days and cell debris was removed by centrifugation. Later, for subsequent infection of a new Vero E6 cell culture flask, 100 µl of the clear supernatant was used. After five days, supernatants were found SARS-COV-2 positive by a conventional qualitative PCR. After harvesting the virus suspension and clearing cellular debris by centrifugation, it was stored at -80°C. The 50% tissue culture infective dose (TCID50) was calculated after determining viral titers by endpoint dilution assay. 

Then, a viral stock at a concentration of 5 x 10^6 TCID50/ml was irradiated with UV light for up to 30 minutes. Separate or combined irradiation with UVC (254 nm) and/or UVA (365 nm) of 600 µl virus stock was performed in 24-well plates. The UV light source was placed 3 cm above the bottom of the plate. The light intensity for UV-C (254 nm) was 1940 µW/cm2 and for UVA (365 nm) was 540 µW/cm2 at a distance of 3 cm, as measured by radiometric analysis. This implies that the applied light dose was 1.94 mJ/cm^2/s for UV-C and 0.54 mJ/cm^2/s for UVA, with µW = 10-6 J/s. Later, the samples irradiated with UVA were taken after 0, 3, 6, 9, 12, 15 minutes, and that of UV-C irradiation after 0, 1, 2, 3, 6, 9, and 15 minutes. Each sample’s TCID50/ml was determined by endpoint dilution. 

According to the authors, high viral loads of 5 x 10^6 TCID50/ml SARS-COV-2 were completely inactivated by a UV-C dose of 1048 ml/cm^2 in just 9 minutes. Moreover, 50% of the virus was inactivated after just 1.4 minutes of UV treatment, as calculated by nonlinear regression. One log reduction of the viral load was observed after 9 minutes of irradiation with an emitted dose of 292 mJ/cm^2. However, a 9-minute exposure to UV-C ( emitted UV-C dose of 1048 mJ/cm^2) resulted in the complete inactivation of the virus. Therefore, according to the authors, UV-C irradiation is a more effective method of inactive SARS-COV-2

Therefore, the observation and experimentation done by the authors prove that SARS-COV-2 is highly susceptible to irradiation with UV light. The authors hence conclude that UV-C, inarguably, is a suitable disinfection method for SARS-CoV-2 

All ultraviolet disinfection products pose a UV radiation hazard. Use only as directed. Protect eyes and skin from exposure to UV light.