The specific wavelength of UV light is a safe and effective way to kill the SARS-CoV-2 virus

A specific wavelength of ultraviolet (UV) light is not only extremely effective at killing the virus that causes COVID-19, but is also safer for use in public spaces, according to new research from the University from Colorado to Boulder.

The study, published this month in Applied and environmental microbiology, is the first to comprehensively analyze the effects of different wavelengths of UV light on SARS-CoV-2 and other respiratory viruses, including the only wavelength that is safer for living things to which living things are exposed to unprotected.

The findings, which the authors call a “game changer” for the use of UV light, could lead to new affordable, safe and highly effective systems for reducing viral spread in crowded public spaces like airports and theaters. the concert.

Of almost all the pathogens we have studied, this virus is by far one of the easiest to kill with UV light. It takes a very low dose. This indicates that UV technology could be a very good solution to protect public spaces. “

Karl Linden, senior author, professor of environmental engineering

UV light is naturally emitted by the sun, and most forms are harmful to living things, as well as to microorganisms, such as viruses. This light can be absorbed into an organism’s genome, tie it up and prevent it from reproducing. These harmful wavelengths from the sun, however, are filtered out by the ozone layer before reaching the earth’s surface.

Some common products, like fluorescent tube lights, use artificial UV light, but a white phosphor coating on the inside protects people from UV rays.

“When we remove this coating, we can emit these wavelengths and they can be harmful to our skin and our eyes, but they can also kill pathogens,” Linden said.

Hospitals are already using UV light technology to disinfect surfaces in crowded spaces, using robots that can shine UV light in operating theaters and patient rooms between uses. .

And there are plenty of gadgets on the market today that clean everything from cell phones to water bottles with UV light. But safety protocols are still being developed by the FDA and EPA. Linden cautions against the use of personal devices or “germicides” in which a person is exposed to UV light.

The new findings are unique, he said, because they strike the sweet spot between UV light which is relatively safe for humans and harmful for viruses, especially the one that causes COVID-19.

“It can be a game-changer for the public use of UV light in indoor spaces,” Linden said.

Death by exposure

For the study, Linden and his team compared different UV wavelengths side-by-side using standardized methods developed in the UV light industry.

“We thought, let’s unite and make a definitive statement on the UV exposure required to kill SARS-CoV-2,” Linden said. “We wanted to make sure that if UV light is used to control disease, you are delivering the right dose that protects human health and human skin, but will also kill these pathogens.”

The opportunity to do this kind of work is rare, as there are extremely stringent safety standards required to work with SARS-CoV-2. So Linden and Ben Ma, postdoctoral fellow in Linden’s research group, collaborated with virologist Charles Gerba of the University of Arizona, in a lab licensed to work with the virus and its variants.

The researchers found that while the virus was sensitive enough to UV light in general, a specific far-ultraviolet C wavelength at 222 nanometers was particularly effective. Created by what is called a krypton chloride excimer lamp, powered by molecules moving between different energy states, this wavelength is of very high energy. Therefore, it is capable of inflicting greater damage to viral proteins and virus nucleic acids compared to other UV-C devices, as well as being blocked by the upper layers of human skin and eyes, this which means he has limited health or not. effects at doses capable of killing viruses.

“Not only is it safe, but it’s also the most effective,” Linden said.

The role of UV disinfection today

UV light in various forms has been widely used since the beginning of the 20th century to disinfect water, air and surfaces. As early as the 1940s, it was used to reduce the transmission of tuberculosis in hospitals and classrooms, by lighting the ceiling to disinfect the air circulating in the room. Today it is used not only in hospitals, but in some public toilets and airplanes when there is no one in these spaces.

In a recent white paper published by the International UV Association, “Far UV-C Radiation: Current State of Knowledge,” which accompanies the new study, Linden and his co-authors argue that this safer wavelength of light Far UV-C could serve as a key mitigation measure against current and future pandemics, in addition to improved ventilation, mask wear and vaccination.

Linden imagines systems that could either turn on and off in interior spaces to regularly clean the air and surfaces, or create a permanent and invisible barrier between teachers and students, customers and service workers, and people in spaces where social distancing is not possible, to disinfect the air.

UV light disinfection can even compete with the positive effects of improved indoor ventilation by providing protection equivalent to increased air changes per hour in a room. It is also much cheaper to install UV lamps than to upgrade an entire HVAC system.

“There is an opportunity here to save money and energy while protecting public health in the same way. It’s really exciting,” said Linden.