Researchers at Hiroshima University offered first proof that UVC light with a 222 nm wavelength, which many claim to be safer for human and animals, can effectively kills the SARS-CoV-2 virus, pathogen of COVID-19.

The study was published in the American Journal of Infection Control on September 4, 2020, titled “Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination.” The article demonstrated the results of an in vitro experiment of the research team which showed that 99.7% of the SARS-CoV-2 viral culture was killed after a 30-second exposure to 222 nm UVC irradiation at 0.1 mW/cm2.

(Image: Hiroshima University)

Tests were conducted using Ushio’s Care222TM krypton-chloride excimer lamp. A 100 microliter solution containing the virus (ca. 5 × 106 TCID50/mL) was spread onto a 9-centimeter sterile polystyrene plate. The researchers allowed it to dry in a biosafety cabinet at room temperature before placing the Far-UVC lamp 24 centimeters above the surface of the plates.

Other studies involving 222 nm UVC, also known as “far UVC,” have so far 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. A nanometer is equivalent to one billionth of a meter.

The researchers, however, suggest further evaluation of the safety and effectiveness of 222 nm UVC irradiation in killing SARS-CoV-2 viruses in real-world surfaces as their study only investigated in vitro efficacy.