Can a beam of light really save us from the virus?

It has long been established that exposure to UV light kills bacteria and viruses. UV light is regularly used to sterilise water, as well as rooms and equipment in hospitals and laboratories, killing any pathogens (microorganism like viruses that cause disease).

Scientist at Columbia University, New York, have recently published work showing that exposing coronaviruses to a certain type of ultraviolet light, called UVC, can result in 99.9% inactivation of the virus (Doremalen et al., 2020). Tests also showed that this form of UVC light is unable to cause the same damage to our cells. UVC lamps could, therefore, potentially be an easy and quick way of stopping the transmission of the COVID-19 virus in public places. But are UVC lamps used in this way really safe?

What is Ultraviolet Light?

We are all familiar with visible light as a form of radiation that we can detect with our eyes. Ultraviolet (UV) light is a form of radiation that is not visible to the naked eye.

The electromagnetic spectrum covers a wide range of electromagnetic radiation that differ in the amount of energy they have. This energy is usually associated with particles called photons. Radio waves at the end of the spectrum have photons with low energies. The amount of photon energy then increases along the spectrum to microwaves, infrared, visible light, ultraviolet, X rays, and finally, gamma rays which have the most energetic photons (see Figure 1 below).

Figure 1: Electromagnetic Spectrum

Electromagnetic radiation is measured in energy (electron volts), frequency (hertz) or wavelength (meters). The lower the energy the longer the wavelength. Visible light, which is the only part of the electromagnetic spectrum we can see, has a wavelength between 400 nm (violet) to 700 nm (red; 1 nm = 10-7 cm).

UV Light: UVA, UVB and UVC

A natural source of UV light is the sun. Long exposure to the sun’s UV rays will cause skin to tan and burn. Over exposure to UV light can result in premature ageing and skin cancers. See our blog posts on ‘Sunlight and Your Skin’ and ‘5 Positive Effects of Being in the Sun’ to learn more.

As you can see in Figure 1, UV light has more energy and shorter wavelength than visible light with a range of 100-400 nm. UV light is classified into three groups based on their wavelength:

• UVA has the lowest energy with a wavelength between 315-399 nm.

• UVB has a wavelength between 280-314 nm, and

• UVC with the highest energy has a wavelength between 100-279 nm.

The ozone layer and atmosphere will absorb all of the UVC before it reaches the Earth’s surface, as well as most of the UVB radiation. UVA is not absorbed, and though it has less energy that UVB and UVC, it is able to penetrate our skin and can lead to skin cancers.

Germicidal UVC Irradiation

Germicidal UVC irradiation has long been used in hospitals, dental surgeries and laboratories as an effective treatment for sterilisation. The UVC radiation inactivates, i.e. destroys, antibiotic-resistant bacteria and viruses by damaging their genomes (the genetic information essential for its survival) (Kerr et al., 1998, Budowsky et al., 1981). Without their genomes, these pathogens cannot make the proteins they need to function or reproduce.

Germicidal UVC lamps have an emission peak of about 254 nm. Unfortunately, this wavelength of UVC radiation is also a hazard to human health. Short exposure can cause reddening of the skin and conjunctivitis in the eyes, with longer exposures resulting in skin cancers and eye diseases. This means that sterilisation by germicidal UVC irradiation can only take place in unoccupied rooms or while wearing full protective clothing.

Far-UVC Light

More recent work has shown that UVC with a wavelength range of 200-222 nm is still able to kill antibiotic-resistant bacteria and viruses without damaging human cells (Buonanno et al., 2017). This far-UVC light has a limited penetration distance, which means it can cross through these small microbes <1 mm (1 mm = 0.0001 cm), reaching their nucleic acid genome and destroying it. But as human cells are much larger (10-25 mm), most of the 222 nm UVC light is absorbed by the proteins in the cytoplasm before it reaches the cell nucleus containing the genome.

Our skin also gives us natural protection as far-UVC light cannot pass through the outermost dead layer of the skin, the stratum corneum, nor the outer layer of the eye. Far-UVC light, therefore, promises to be safer for sterilisation than germicidal UVC lamps in occupied areas with no health hazard or additional protection needed.

How can Far-UVC Light help with the COVID-19 Pandemic?

Germicidal UVC lamps usually emit at 254 nm. They were currently limited to sterilising rooms and equipment already contaminated with the COVID19 virus, SARS-CoV-2, effectively inactivating the virus. Recently, other establishments have begun using these germicidal UVC lamps to disinfect their areas. For example, transport authorities are starting to use germicidal UVC lamps to regularly disinfect their vehicles like buses in Shanghai, China.

The main transmission of SARS-CoV-2 is through direct contact and airborne routes. SARS-CoV-2 released in aerosols through breathing, sneezing, coughing and talking, has been shown to stay viable in the air for up to 3 hours. On surfaces such as plastic, stainless steel and cardboard, the virus remains viable for longer, between 8 and 72 hours (Doremalen et al., 2020). This is summarised in Table 1 below. Table 1 also shows the half-life of the virus, which is simply the time taken for the amount of virus to drop by half, on the different materials.

While a lot of research is currently focused on developing vaccines and finding a cure for COVID-19, recent published work has looked at the effect of far-UVC light on killing the virus in the air or on surfaces in public places. This is not a new idea. Research over the past decades have looked into using UVC technologies as an effective way of stopping viruses that cause seasonal epidemics, like the influenza virus, as well as pandemics. However, focus since shifted to the use of vaccines and modern medicine to control and cure these.

Far-UVC light has been shown to be efficient at inactivating airborne H1N1 influenza virus by 95% (Welch et al., 2018). More recent work by the same group focuses on the effects of far-UVC light on coronaviruses (Buonanno et al., 2020). They found 99.9% inactivation of aerosolised human coronaviruses when exposed to far-UVC light for only 25 minutes (see Table 2). These results would indicate that exposure to far-UVC light efficiently kill infectious airborne coronaviruses carried by aerosols. Though they did not use the SAR-CoV-2 itself, the results would still apply as all coronaviruses have a similar genome size.

So, What’s the Final Verdict?

Current use of germicidal UVC lamps as outlined above continue to be the most efficient way of inactivating infectious virus in the air and on surfaces. In addition, they are increasingly being installed in occupied areas to kill the airborne virus. Air purification systems already exist with these UVC lamps hidden within ventilation air ducts so that they are completely shielded from people, or installed very high in the ceiling above people’s head. The latter will still have the risk of causing redness and conjunctivitis if not installed within guidance, depending upon distance and time people are exposed, though this will go away after a few days. Interestingly, Brussel expo are currently installing 1200 air purifier devices with germicidal UVC lamps to reduce airborne risk of infection and increase confidence to their clients, customers and visitors when they reopen.

However, research has shown that 220 nm far-UVC light also efficiently kills bacteria and viruses. And as our skin acts as a natural barrier of protection against this radiation, far-UVC light is safer to use than current germicidal 254 nm UVC lamps.

Far-UVC technology, therefore, has the potential of being a safe and effective tool in reducing the spread of airborne viruses. Their use in a variety of public areas would help to curb the person-to-person spread of COVID-19 by individuals who are asymptomatic; those who are infected with SARS-CoV-2 but have none of the COVID-19 symptoms. It also has the potential to limit the spread of future pandemics.

But wait. This doesn’t mean that everyone should rush to buy a UVC lamp. Most UVC lamps sold are the germicidal 254 nm UVC lamps that have no established role in household disinfection. In fact there have already been reports of injuries due to high UVC exposure from these lamps in an attempt to inactivate SARS-CoV2 at home (Leung & Ko, 2020). And the WHO have issued a warning against using UV light to disinfect your skin (WHO Myth Busters).

There are newer UVC lamps available that promise to be less dangerous by emitting UVC at 220 nm, these have not been tested efficiently for safety. Keep in mind that all the research on far-UVC light inactivating viruses have been done in the lab, on cells in a dish, not on actual people. Future risk to health due to repeated or long exposure time would need further investigation to ensure that it is safe for general use. It’s also worth noting that there are a lot of good bacteria out there in the environment and killing them all will have huge biological consequences to our lives.

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