By Jennifer Lauren Lee/NIST
To disinfect a surface, you can illuminate it with a blast of ultraviolet (UV) light, which is bluer than the human eye can see. But to specifically inactivate SARS-CoV-2, the virus that causes COVID-19, which wavelengths are best? And how much radiation is enough?
Answering those questions requires scientists to overcome two main obstacles. First, they need to separate the virus completely from extraneous substances in the environment. Second, they need to illuminate the virus with a single wavelength of UV light at a time, with minimal changes to the experimental setup between tests.
A recent collaboration between the National Institute of Standards and Technology (NIST) and the National Biodefense Analysis and Countermeasures Center (NBACC), a U.S. Department of Homeland Security Science and Technology Directorate laboratory, overcame both these obstacles and completed what may be the most thorough test ever conducted of how several different UV and visible wavelengths affect SARS-CoV-2.
In a new paper published this week in Applied Optics, the collaborators describe their novel system for projecting a single wavelength of light at a time onto a sample of COVID-19 virus in a secure laboratory. Classified as Biosafety Level 3 (BSL-3), the lab is designed for studying microbes that are potentially lethal when inhaled. Their experiment tested more wavelengths of UV and visible light than any other study with the virus that causes COVID-19 to date.
So, what is SARS-CoV-2’s kryptonite? As it turns out, nothing special: The virus is susceptible to the same wavelengths of UV light as other viruses such as those that cause the flu. The most effective wavelengths were ones in the “UVC” range between 222 and 280 nanometers (nm). UVC light (full range from 200 to 280 nm) is shorter than the UVB wavelengths (280 to 315 nm) that cause sunburn.
Researchers also showed that the virus’s surroundings can have a protective effect on the virus. In the study, it took a smaller UV dose to inactivate viruses when they were placed in pure water than when they were placed in simulated saliva, which contains salts, proteins and other substances found in actual human saliva. Suspending the virus in simulated saliva creates a situation similar to real-world scenarios involving sneezes and coughs. This may make the findings more directly informative than those of previous studies.
“I think one of the big contributions of this study is that we were able to show that the kind of idealized results we see in most studies don’t always predict what happens when there’s a more realistic scenario at play,” said Michael Schuit of NBACC. “When you have material like the simulated saliva around the virus, that can reduce the efficacy of UV decontamination approaches.”
Manufacturers of UV disinfection devices and regulators can use these results to help inform how long surfaces in medical settings, airplanes, or even liquids should be irradiated to achieve inactivation of the SARS-CoV-2 virus.
“Right now, there’s a big push to get UVC disinfection into the commercial atmosphere,” said NIST researcher Cameron Miller. “Long-term, hopefully this study will lead to standards and other methodologies for measuring UV dose required to inactivate SARS-CoV-2 and other harmful viruses.”
This project built upon earlier work the NIST team did with another collaborator on inactivating microorganisms in water.
Shed a Little Light
Depending on the wavelength, UV light damages pathogens in different ways. Some wavelengths can damage microbes’ RNA or DNA, causing them to lose the ability to replicate. Other wavelengths can break down proteins, destroying the virus itself.
Even though people have known about UV light’s disinfection abilities for more than a hundred years, there’s been an explosion in UV disinfection research in the past decade. One reason is that traditional sources of UV light…