American scientists and engineers experimenting with LED lamps have picked up such wavelengths that kill the coronavirus not only on the surfaces of objects and in rooms but also penetrate into human cells, infecting the virus there as well. The article was published in the journal Scientific Reports.

Ultraviolet light is widely used in hospitals to sterilize rooms and instruments. Previously, in several scientific papers, their authors noted that ultraviolet radiation is also effective for inactivating coronaviruses that are on the surface of objects in the aerosol or liquid phase. When the RNA virus absorbs UV photons, pyrimidine dimers are formed, preventing further replication.

However, the possibilities of using ultraviolet light as a therapeutic agent are limited since, at high doses of radiation, it can cause damage to mammalian genomes, causing mutations and disrupting DNA. Therefore, for the inactivation of RNA and DNA viruses, the photobiomodulation method, or light therapy, is often used based on the use of visible spectrum or near-infrared light. However, it is less effective than ultraviolet light.

American scientists have identified a safe range of blue waves of a certain density for humans, which kill the SARS-CoV-2 virus, regardless of whether it is inside a living cell or outside it.

To find out how such light is safe for human cells, the authors created three-dimensional cell models from donor cells obtained from the bronchi and trachea of the same person. The created models, having a thickness of three to four layers of mucociliary epithelial cells, were exposed to light at wavelengths of 385, 405, and 425 nanometers.

The first, belonging to the A-band of UV light, showed a decrease in cell viability by 50 percent, the second – by 25 percent, while waves of 425 nanometers in length, almost completely located in the visible part of the spectrum, did not harm tissues.

To confirm the results, the researchers tested the effect of blue light with a wavelength of 425 nanometers on Vero E6 cells, which are commonly used to assess the cytotoxic properties of potential agents against SARS-CoV-2. It turned out that even low doses of such light are enough to reduce the viral load, and higher doses showed a 99.9 percent reduction in infection without a visibly negative impact on the viability of uninfected cells.

The authors also selected optimal parameters, including wavelengths and irradiation time, for inactivation of other beta-coronaviruses, such as SARS-CoV-1 and MERS. At the same time, significantly higher doses of light were required to inactivate the latter. To eliminate the subjective factor, the results of all measurements were checked in two independent laboratories.

The researchers hope that their new development will have a significant benefit in the fight against the coronavirus pandemic, especially in countries and regions where there are not enough vaccines.