Ubiquitous Far-Ultraviolet Light Could Control the Spread of Covid-19 and Other Pandemics

Roko Mijic, Alexey Turchin

Epistemic sta­tus: Many differ­ent un­cer­tain­ties here, but the idea has some good ev­i­dence in fa­vor of it and a high po­ten­tial pay­off.

Tl;dr: We should ur­gently in­ves­ti­gate putting spe­cial hu­man-safe Far-UVC lamps all over our built en­vi­ron­ment to ‘kill’ virus par­ti­cles whilst they are in the air, thereby vastly re­duc­ing covid-19 spread.

In­spired by: https://​​www.na­ture.com/​​ar­ti­cles/​​s41598-018-21058-w

One of the most promis­ing and ne­glected ideas for com­bat­ing the spread of covid-19 is the use of ubiquitous ul­tra­vi­o­let light in our built en­vi­ron­ment (trains, offices, hos­pi­tals, etc). Ul­travi­o­let light is already be­ing used as a dis­in­fect­ing agent across the world; it goes by the acronym UVGI—“Ul­travi­o­let ger­mi­ci­dal ir­ra­di­a­tion”. The en­er­getic pho­tons of UVC light break chem­i­cal bonds in DNA and kill/​in­ac­ti­vate both viruses and bac­te­ria.

Ul­travi­o­let light on earth ex­ists on a spec­trum be­tween 200nm and 400nm. Light above 400nm is blue visi­ble light. Light be­low 200nm is called “vac­uum UV” be­cause it is strongly ab­sorbed by the oxy­gen in or­di­nary air and there­fore can­not ex­ist ex­cept in a vac­uum or some other non-air medium. Within the 200-400nm range we have UVA, UVB and UVC, and at the short-wave edge of the UVC band we have “Far-UVC”, from roughly 200nm–220 nm.

Safety considerations

Hu­man be­ings are also vuln­er­a­ble to UV ra­di­a­tion. It causes skin can­cer and se­ri­ous eye dam­age.

How­ever, re­cent re­search sug­gests that the Far-UVC band is ac­tu­ally safe for hu­man skin be­cause it can­not pen­e­trate through the thin layer of dead skin cells on the sur­face of our skin.

This means that it might be pos­si­ble to mount a long-term re­sponse to covid and other pathogens by con­stantly illu­mi­nat­ing our built en­vi­ron­ment with light from speci­fi­cally the Far-UVC band. If the Far-UVC light is in­deed safe for hu­mans, the Far-UVC could be on at all times and could de­stroy or de­ac­ti­vate viral par­ti­cles be­fore they can spread from per­son to per­son.

Why hasn’t this already been con­sid­ered by rele­vant au­thor­i­ties? Far-UVC ap­pears in a liter­a­ture re­view by WHO, but it is not cur­rently be­ing acted upon as the amount of ev­i­dence in fa­vor of safety and effi­cacy is small.

There is some un­cer­tainty about whether Ozone gen­er­a­tion by this band (200nm-220nm) would be prob­le­matic. Ozone is not great for your health. How­ever, it seems to be the case that the 200-220nm band is not a strong pro­ducer of Ozone. In ad­di­tion, UV degra­da­tion of sur­faces might re­sult from chronic UV ex­po­sure.

Balanc­ing harms of ac­tion and inaction

Even if Far-UVC is some­what harm­ful it might still be a good idea to im­ple­ment. Small harms from Far-UVC light might be much less bad than large harms from covid-19, or from the eco­nomic dam­age caused by the lock­down which one au­thor es­ti­mates to be roughly $10 mil­lion per minute, plus much per­sonal hard­ship which will be caused by the forth­com­ing re­ces­sion.

Fur­ther­more, UV light is eas­ier to defend a per­son against than a virus. Sun-creams, cloth­ing and eye­wear that defend against UVC may be less bad than a semi-per­ma­nent lock­down or an ex­po­nen­tially grow­ing covid-19 out­break that re­sults in mil­lions or tens of mil­lions of deaths. UV in the built en­vi­ron­ment could even be man­aged in­tel­li­gently—com­puter vi­sion could iden­tify where the peo­ple were and turn on UV lights only in un­oc­cu­pied ar­eas, though such a pro­ject would at best be ready by the start of 2021 (and then only with wartime lev­els of effort and pur­pose).

If the safety claims of Far-UVC are par­tially true rather than fully true, a com­bi­na­tion of us­ing Far-UVC with phys­i­cal pro­tec­tion like eye­wear may still cause only ac­cept­able losses to can­cer and eye dam­age. In the longer term, such “al­most safe” Far-UVC could be com­bined with in­tel­li­gent man­age­ment at var­i­ous lev­els of gran­u­lar­ity; imag­ine a lift that is bathed in Far-UVC ev­ery time peo­ple leave it, or “walls” of Far-UVC sep­a­rat­ing peo­ple that au­to­mat­i­cally turn off mo­men­tar­ily when a per­son walks through them. The ul­ti­mate sys­tem might even ad­just the power of the Far-UVC us­ing AI.

Epi­demiolog­i­cal considerations

Even an ideal Far-UVC solu­tion that was harm­less to hu­mans, 100% lethal to covid-19 par­ti­cles and easy to de­ploy at scale might not be suffi­cient to re­duce R to ex­actly 0. But the key ques­tion is whether it could re­duce R be­low 1 whilst also al­low­ing most eco­nomic ac­tivity. An easy pre­limi­nary ex­per­i­ment to run would be to put virus sam­ples in mouse cages—per­haps in aerosolized form—treat some cages with Far-UVC, leave other cages alone, see if in­fec­tion rates go down in the treated cages.

This is an im­por­tant source of un­cer­tainty and fur­ther re­search is needed.

Scaleup considerations

Even a perfect sys­tem is use­less if it can­not be scaled up and im­ple­mented across the globe. Far-UVC can be pro­duced from Kryp­ton Chlo­ride (Kr-Cl) Ex­cimer Lamps, but mod­ern Alu­minium Nitride (AlN) Far-UVC LEDs are a bet­ter solu­tion for the long term. In the even longer term, col­li­mated Far-UVC could be pro­duced by lasers. This is an im­por­tant source of un­cer­tainty and fur­ther re­search and ex­pert in­put is needed.

Power con­sid­er­a­tions:

The amount of Far-UVC en­ergy re­quired to kill 99% of the viral par­ti­cles is es­ti­mated to be around 20J/​m^2. With a power of, say 5W/​m^2, a sys­tem would need 4 sec­onds to mostly ster­il­ize a viral aerosol that could travel from per­son to per­son. How­ever a lower power sys­tem would still have some benefits—we know that peo­ple can be in­fected by air that was con­tam­i­nated 30 min­utes ear­lier. Higher power in these wave­lengths could be difficult to achieve with Kr-Cl Ex­cimer Lamps as the over­all effi­ciency from elec­tric­ity to Far-UVC is ~10% (White’s Hand­book of Chlo­ri­na­tion and Alter­na­tive Dis­in­fec­tants, un­der figure 17.14). AlN Far-UVC LEDs would likely have a much higher con­ver­sion effi­ciency.

Generality

One of the great­est benefits of Far-UVC is that it would be a very gen­eral weapon against pathogens. Far-UVC kills/​de­ac­ti­vates bac­te­ria, viruses and other pathogens. MRSA, C-DIFF, in­fluenza, etc are all kil­led by UVC, as is the next prob­le­matic pathogen, what­ever it is.

Summary

There are many differ­ent rea­sons that Ubiquitous Far-UVC might not work out, but if it did work out it could have huge benefits. For this rea­son the au­thors be­lieve that it should get more at­ten­tion at this crit­i­cal time. Scaleup and safety and effi­cacy tri­als must all be car­ried out as quickly as pos­si­ble, prefer­ably in par­allel. More im­por­tantly, the idea needs more at­ten­tion from ex­perts in the rele­vant fields—UV physics, epi­demiol­ogy, and peo­ple who study the etiol­ogy of skin can­cers. As of writ­ing there are re­ports that the US gov­ern­ment es­ti­mates the epi­demic could last for 18 months, so a plan like Far-UVC that will take months to im­ple­ment may still be a crit­i­cal com­po­nent of a re­sponse later this year.

Ap­pendix. Other ways to use UV light to fight coronavirus

One of the ex­pla­na­tions of the flu and other in­fec­tions sea­son­al­ity is that the Sun’s UV kills viruses. How­ever, peo­ple spend a lot of time in­doors even dur­ing sum­mer, and es­pe­cially dur­ing self-iso­la­tion. Most of our in­fec­tions are hap­pen­ing in­doors: at home, in trans­port and in work­ing places. UV from Sun could be part of the ex­pla­na­tion of the lower in­stances of coro­n­avirus in south­ern coun­tries.

If we re­place light bulbs ev­ery­where with light sources which also emit UV light of some spe­cial wave­length, we will kill most of the air­borne viruses and will clean fomites. Thus, we will cre­ate ar­tifi­cial sum­mer ev­ery­where and will lower R0 of coro­n­avirus be­low 1.

The main ob­sta­cles are the du­ra­tion of ex­po­si­tion and pos­si­ble harm to peo­ple. Re­cently in Moscow 20 chil­dren had burns in their eyes af­ter a school teacher for­got to turn off the UV cleaner in the class­room.

There are sev­eral other ideas, be­sides Far-UVC light, to pre­vent hu­man eye and skin dam­age:

1) In­tel­lec­tu­ally con­trol­led UV light­ing. UV light source turns on the max­i­mum level when there are no peo­ple in the room. We already have mo­tion de­tec­tors for light­ing, but here they will work in re­verse. Light with mo­tion de­tec­tion could also di­rect light in di­rec­tions, where there is no mo­tion, so no peo­ple. On the video, one can see UV light sources on sale with mo­tion de­tec­tors:

The power of light could be tem­porar­ily in­creased af­ter the sound of sneez­ing. But it will make all the sys­tem more com­plex and its large-scale im­ple­men­ta­tion will take longer time. If Kryp­ton Chlo­ride Ex­cimer bulbs are used, their life­time is not great, so they can’t run con­stantly. But if we can get the Alu­minium Nitride LEDS then life­time and effi­ciency will be bet­ter.

2) Not “too strong” sources of UV, which are pro­duc­ing Sun’s in­ten­sity of UV and which act mostly on fomites. As we know, hu­mans can sur­vive at least 1 hour of sun­light UV ex­po­sure with­out strong dam­age (on beaches). We could use it as a refer­ence point to cal­ibrat­ing UV sources.

3) Strong UV light­ing + gloves. Every­one will wear gloves, masks and glasses out­side. In that case, no skin will be ex­posed to the UV light­ing (and to viruses). Wear­ing PPE will be effec­tive any­way. Women in the East are wear­ing full cover clothes, and they are ok.

4) Wear­able head­light UV will di­rect UV light in the op­po­site di­rec­tion to the per­son’s eyes but will cover ev­ery­thing he in­hales or touches, as well as his hands. The light will be strongest near the hu­man face (but not af­fect­ing the face), and will at­tack droplets which the per­son is about to in­hale. How­ever, the light will dis­si­pate in the dis­tance of 1- 2 me­ters to safer lev­els. UV head­lamps already ex­ist and on sale, but may be not strong enough for dis­in­fec­tion. It will be es­pe­cially effec­tive if wear­ables Far UVC light sources will be used.

5) UV flash­light—Torch that emits UV ra­di­a­tion in a wide beam. Runs off main power. Could be used by clean­ers as an ad­di­tional step when clean­ing sur­faces.

Pros:

  1. Sim­pler, eas­ier, cheaper and faster to build than other solutions

  2. Less harm to peo­ple, as UV light can be di­rected, and is not always on

  3. Prov­ing ground (an MVP, in startup terms) for more ad­vanced implementations

  4. Mo­bile; could be used in mul­ti­ple locations

Cons:

  1. Less effec­tive than always on UV lights and lamps

  2. Re­quires ad­di­tional time/​effort on top of nor­mal clean­ing routines

Ar­tifi­cial light ex­ists cur­rently al­most ev­ery­where, where con­tem­po­rary hu­mans live: in homes, in any shop, in cars and even on the streets. All we need is to re­place elec­tric lamps. Large amounts of lamps could be man­u­fac­tured in 0.5-1 year, and smaller amounts for crit­i­cal places like ele­va­tors in the even shorter no­tice.

How­ever, there is a prob­lem of ac­tual test­ing the tech­nol­ogy un­til it will be ap­proved as safe and effec­tive by the FDA. It is tech­ni­cally difficult to make deep UV (220nm) light-emit­ting diodes.

A good start will be to put UV lights in the places of short use: ele­va­tors, shops, re­strooms.

It is much more con­ve­nient to wear pro­tec­tion against light than pro­tec­tion against viruses, and af­ter a few months of lock­down, the idea of re­turn­ing to al­most nor­mal life but with sun cream and/​or gloves will be quite nice.

References

Welch, D., Buo­nanno, M., Grilj, V. et al. Far-UVC light: A new tool to con­trol the spread of air­borne-me­di­ated micro­bial dis­eases. Sci Rep 8, 2752 (2018). https://​​doi.org/​​10.1038/​​s41598-018-21058-w

Nar­ita K, Asano K, Mo­ri­moto Y, Igarashi T, Nakane A (2018) Chronic ir­ra­di­a­tion with 222- nm UVC light in­duces nei­ther DNA dam­age nor epi­der­mal le­sions in mouse skin, even at high doses. PLoS ONE 13(7): e0201259. https://​​doi.org/​​ 10.1371/​​jour­nal.pone.0201259

Willie Tay­lor, Emily Camil­leri, D. Levi Craft, Ge­orge Korza, Maria Rocha Grana­dos, Jal­iyah Peter­son, Re­nata Szcz­pa­niak, San­dra K. Wel­ler, Ralf Moel­ler, Thierry Douki, Wendy W.K. Mok, Peter Set­low DNA dam­age Kills Bac­te­rial Spores and Cells Ex­posed to 222 nm UV Ra­di­a­tion Ap­plied and En­vi­ron­men­tal Micro­biol­ogy Feb 2020, AEM.03039-19; DOI: 10.1128/​AEM.03039-19

Colorado com­pany uses UV light­ing tech­nol­ogy to kill 99.9 per­cent of bac­te­ria and viruses. Fox Den­ver, 7 Macrh 2020

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