Apr 24 2020

UVC and Covid-19

On this week’s SGU (which will go online tomorrow) I talked about the use of ultraviolet light as an anti-viral strategy. I wasn’t planning on also writing about it, but then the president decided to make some incredibly dubious comments about is, so I thought I would address it here. Here’s what he said:

“So, supposing we hit the body with a tremendous – whether it’s ultraviolet or just very powerful light,” the president said, turning to Dr Deborah Birx, the White House coronavirus response co-ordinator, “and I think you said that hasn’t been checked but you’re going to test it.

“And then I said, supposing you brought the light inside of the body, which you can do either through the skin or in some other way. And I think you said you’re going to test that too. Sounds interesting,” the president continued.

He also made some ever sillier comments about injecting people with disinfectant – both comments commit the same error, confusing an external treatment for an internal one., and also suggesting that treatments meant for objects be used on people. So what is the deal with UV light as an antiseptic? The antiseptic effects of UV light have been known for a long time. In 1878, Arthur Downes and Thomas P. Blunt published the first paper describing this effect. Ultraviolet light has enough energy to cause tissue damage – that is why you get a sunburn if you get too much sun exposure.

UV light is electromagnetic radiation between visible light and X-rays on the spectrum, from 10-400 nm wavelength. These are higher energy waves than visible light, with enough energy to cause chemical reactions and damage DNA. UV light is further divided into biological relevant categories of UVA (400-315 nm), UVB (315-280 nm) and UVC (280-100 nm). The ozone layer filters out 97-99% of UV radiation from 315-200 nm, so the UVB and part of the UVC spectrum. Otherwise the suns rays would be much more harmful. On the Earth’s surface there is about 500 times the intensity of UVA than UVB, and almost no UVC. Biologically, UVA penetrates deeper into the skin and does cause long term aging effects. UVB affects the skin surface but causes sunburns and damage that can lead to skin cancer. UVC could cause extreme damage even with minutes of exposure (depending on the intensity).

The entire spectrum has some antiseptic activity, but the shorter wavelengths are higher energy and more effective. UVC in particular is effective at destroying viruses, by damaging their DNA or RNA. UV light is already in wide use as an antiseptic, in labs, hospitals, and some industrial settings. What is the relevance of all this to COVID-19? Not much, in the short term. UVC is probably as effective against the SARS-Cov2 virus as other viruses, but it needs to be specifically tested. If effective, which is likely, can it be used as part of a sterilization protocol to reduce the spread of the virus? Sure, if used properly and in the appropriate setting. Also, UV equipment used for sterilization is fairly heavy duty, with professional units casting about $1000 at the low end.

However, there are plenty of products aimed at consumers for much cheaper. You can buy a UV box to put your phone or money clip into to sterilize them with UV light from LEDs. Do these work? I don’t know. Consumer Reports had this to say:

“It wouldn’t surprise me if those devices work to inactivate the new coronavirus but there are no studies on that yet, and I don’t know that the gadgets are any more effective than using a disinfectant like isopropyl alcohol or ethyl alcohol,” Schaffner says. UVC light can also be extremely harmful to your eyes and skin if not used properly. For consumers, Schaffner says, “there are more reliable and less expensive ways to disinfect surfaces.”

So it’s plausible there is an effect, but we lack testing. Specifically, I don’t know what the intensity of the light used in such devices is and the length of exposure necessary to be effective. As CR says – alcohol wipes are cheaper and probably just as effective, but the UV devices seem so high-tech. The UVC light that is effective against viruses, however, is extremely damaging to human skin. So under no circumstance should UVC be used as an attempt to disinfect human skin. Don’t use it on your hands (and again, just wash them thoroughly). There is also no way to get the light inside the body, as a treatment for those already infected.

There is, however, one wrinkle to this story – a very recent study showed that using UVC light limited to specifically 222 nm, tested in mice, did not cause damage to skin or eyes. The idea is that this specific frequency is filtered out by the top layers of skin. If this result replicates, and applies to humans (big ifs) then this could be a useful finding. It would not necessary mean that you can shine 222 nm light at people without concern. This was a short term exposure study only. We would need a lot more safety data in humans before specific recommendations could be made. So again, this is a preliminary study in mice, and more research needs to be done.

For now, for the consumer, I don’t think there are any useful products out there based on UV light. This appears to be a more risky and more expensive solution to a problem that already has a cheap and effective solution. And no, we will not be treating Covid-19 by shining UV light into people’s bodies.

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