Published: February 11, 2018

A new study at the Center for Radiological Research at Columbia University Irving Medical Center reports that nonstop low levels of far ultraviolet C (far-UVC) light can kill airborne flu viruses without damaging human tissues.

The results indicate that use of overhead far-UVC light in schools, hospitals, doctors’ offices, airports, airplanes, and other public spaces could provide a potent checkpoint for seasonal influenza epidemics, as well as influenza pandemics and drug-resistant tuberculosis.

It has been known for decades that broad-spectrum UVC light, which has a wavelength of between 200 to 400 nanometers, or nm), is highly effective at killing bacteria and viruses by destroying the molecular bonds that hold their DNA together. This conventional UV light is routinely used to decontaminate surgical equipment.

“Unfortunately, conventional germicidal UV light is also a human health hazard and can lead to skin cancer and cataracts, which prevents its use in public spaces,”

said study leader David J. Brenner, PhD, the Higgins Professor of Radiation Biophysics Professor of Environmental Health Sciences and director of the Center for Radiological Research at Columbia University Irving Medical Center (CUIMC).

Far Ultraviolet C

Several years ago, Dr. Brenner and his colleagues hypothesized that a narrow spectrum of ultraviolet light called far-UVC could kill microbes without damaging healthy tissue, using filtered excimer lamps emitting in the 207 to 222 nm wavelength range.

“Far-UVC light has a very limited range and cannot penetrate through the outer dead-cell layer of human skin or the tear layer in the eye, so it’s not a human health hazard. But because viruses and bacteria are much smaller than human cells, far-UVC light can reach their DNA and kill them,”

he explained.

In previous studies, Dr. Brenner’s team showed that far-UVC light was effective at killing MRSA (methicillin-resistant S. aureus) bacteria, a common cause of surgical wound infections, but without harming human or mouse skin.

Antiviral efficacy of different low doses of 222-nm far-UVC light.
Typical fluorescent images of MDCK epithelial cells infected with influenza A virus (H1N1).
The viruses were exposed in aerosolized form in the irradiation chamber to doses of 0, 0.8, 1.3 or 2.0 mJ/cm2 of 222-nm far-UVC light.
Infected cells fluoresce green (blue = nuclear stain DAPI; green = Alexa Fluor-488 conjugated to anti-influenza A antibody). Images were acquired with a 40× objective.
Credit: David Welch et al, CC-BY

At a price of less than $1,000 per lamp — a cost that would surely decrease if the lamps were mass produced — far-UVC lights are relatively inexpensive.

Airborne Influenza Virus

Influenza virus spreads from person to person mainly through fine liquid droplets, or aerosols, that become airborne when people with flu cough, sneeze, or talk. The new study was designed to test if far-UVC light could efficiently kill aerosolized influenza virus in the air, in a setting similar to a public space.

In the study, aerosolized H1N1 virus — a common strain of flu virus — was released into a test chamber and exposed to very low doses of 222 nm far-UVC light. A control group of aerosolized virus was not exposed to the UVC light.

The custom UV irradiation chamber.
The experimental setup shows many of the necessary components while some elements, such as pumps, filters, and lamps, were omitted to better depict the overall setup.
Credit: David Welch et al, CC-BY

The far-UVC light efficiently inactivated the flu viruses, with about the same efficiency as conventional germicidal UV light.

“If our results are confirmed in other settings, it follows that the use of overhead low-level far-UVC light in public locations would be a safe and efficient method for limiting the transmission and spread of airborne-mediated microbial diseases, such as influenza and tuberculosis. And unlike flu vaccines, far-UVC is likely to be effective against all airborne microbes, even newly emerging strains,”

said Dr. Brenner. The work was supported by the Shostack Foundation and the NIH.