Ultraviolet C light with a wavelength of 222nm effectively kills SARS-CoV-2 and is safe to use around humans, claim researchers in Japan.
The findings from a team at Hiroshima University are said to be the first that prove the efficacy of 222nm UVC light against the virus that causes COVID-19.
According to Hiroshima University, other studies involving 222nm UVC (Far-UVC) have only looked at its potency in eradicating seasonal coronaviruses that are structurally similar to the SARS-CoV-2 but not on the COVID-19-causing virus itself.
An in vitro experiment by HU researchers showed that 99.7 per cent of the SARS-CoV-2 viral culture was killed after a 30-second exposure to 222nm UVC irradiation at 0.1mW/cm2. The study is published in the American Journal of Infection Control.
Tests were conducted using an Ushio Care222 krypton-chloride excimer lamp. A 100µl solution containing the virus (ca. 5 × 106 TCID50/mL) was spread onto a 9cm sterile polystyrene plate. The researchers allowed it to dry in a biosafety cabinet at room temperature before placing the Far-UVC lamp 24cm above the surface of the plates.
A wavelength of 222nm UVC cannot penetrate the outer, non-living layer of the human eye and skin and will not harm the living cells beneath. This makes it a safer but equally potent alternative to the more damaging 254nm UVC germicidal lamps being used increasingly to disinfect healthcare facilities.
Since 254nm UVC harms exposed human tissues, it can only be used to sanitise empty rooms. But 222nm UVC can be a promising disinfection system for occupied public spaces including hospitals where nosocomial infections are possible.
The researchers, however, suggest further evaluation of the safety and effectiveness of 222nm UVC irradiation in killing SARS-CoV-2 viruses in real-world surfaces.