Far-Ultraviolet Light in Public Spaces to Fight Pandemic is a Good Idea but Premature

Also posted on my per­sonal blog.

Tl;dr: Far-ul­tra­vi­o­let light has po­ten­tial as a hu­man-safe ger­mi­cide, but its safety is not es­tab­lished. In par­tic­u­lar, ev­i­dence that it is not car­cino­genic ex­ists for only one of two mechanisms for ul­tra­vi­o­let car­cino­genic­ity. In ad­di­tion, use of far-ul­tra­vi­o­let light in pub­lic spaces to pre­vent the spread of SARS-COV-2 or other pathogens leads to a host of other con­cerns that need to be ad­dressed.

Introduction

In 2017, Na­ture pub­lished a pa­per that in­ves­ti­gated the pos­si­bil­ity of us­ing far-UVC light to com­bat a fu­ture in­fluenza pan­demic. The pa­per went mostly un­no­ticed by non-aca­demics, as is the norm for tech­ni­cal jour­nals, but now with the novel coro­n­avirus and the first pan­demic of its kind in 100 years, the pub­lic at large is pay­ing at­ten­tion to ideas from the fron­tiers and fringes of biol­ogy and medicine. Last month, far-UVC’s safe ger­mi­ci­dal po­ten­tial was the sub­ject of a post by Roko Mijic and Alexey Turchin on LessWrong. They call the use of far UVC in pub­lic spaces “one of the most promis­ing and ne­glected ideas for com­bat­ing the spread of covid-19,” and lament “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.”

I’ve spent the last few weeks ed­u­cat­ing my­self on the liter­a­ture sur­round­ing far-UVC’s safety, and I’ve come to a clear con­clu­sion. Is the use of far-UVC to com­bat pan­demics in gen­eral a good idea? Yes. Should re­search on it be ex­panded? Yes. But us­ing far-UVC in pub­lic spaces to com­bat COVID-19 would be way way way pre­ma­ture.

First, a cou­ple of dis­claimers:

Dis­claimer 1: I am not a biol­o­gist or a doc­tor. I don’t have any­thing near a pro­fes­sional’s ex­per­tise on hu­man biolog­i­cal ques­tions. There may be in­ac­cu­ra­cies or mi­s­un­der­stand­ings through­out this post, al­though of course I’ve done my best.

Dis­claimer 2: My method for re­search tends to be brows­ing Wikipe­dia to find gen­eral in­for­ma­tion, and us­ing Wikipe­dia’s cita­tions and ex­ter­nal links to find more rigor­ous dis­cus­sion of spe­cific in­for­ma­tion. I try to be wary of Wikipe­dia’s short­com­ings—I read talk pages and check cita­tions—but even so, bias and in­ac­cu­racy on Wikipe­dia will in­evitably seep into my per­spec­tive. I’ll leave it up to the reader to de­cide ex­actly how this re­search method af­fects my cred­i­bil­ity.

Ba­sic Bio­phys­i­cal Ar­gu­ment for Safety and Efficacy

Ul­travi­o­let (UV) light is elec­tro­mag­netic ra­di­a­tion that is shorter wave­length (higher en­ergy) than visi­ble light and longer wave­length than X-rays. The UV light that can be found on Earth is bro­ken into three sub­cat­e­gories: UVA, clos­est to visi­ble, (315-380 nm), UVB (315–280 nm), and UVC (280-200 nm). Although the sun emits light in all three UV cat­e­gories, as well as visi­ble and in­frared (IR), not all the light reaches us on the sur­face. UVC is ab­sorbed by the ozone layer, and the only UVC light we ex­pe­rience comes from ar­tifi­cial sources.

UVC light has been used as a ger­mi­cide since the mid-20th cen­tury, but not in pub­lic spaces. Nu­cleic acids (DNA and RNA) strongly ab­sorb UVC light, which means that when UVC light en­ters a cell, pho­tons will hit ge­netic ma­te­rial, dam­ag­ing or de­stroy­ing it. This makes UVC light a strong ger­mi­cide, but it also means that it is highly car­cino­genic, catarac­to­genic, and toxic to hu­man cells. Ac­cord­ingly, its use as a ger­mi­cide is rel­e­gated solely to en­vi­ron­ments like wa­ter san­i­ta­tion sys­tems where hu­mans won’t be ex­posed.

How­ever, there is still hope that UVC could be used safely in hu­man en­vi­ron­ments in the fu­ture. There is some ev­i­dence that a cer­tain band of UVC light, “far-UVC” (200-220 nm) is safe for hu­mans while re­main­ing toxic to pathogens.

The ba­sic bio­phys­i­cal ar­gu­ment for why far-UVC might be safe hinges on the fact that mam­mals are much big­ger than bac­te­ria and viruses. This band of UVC light is ab­sorbed by pro­teins, as shown in the fol­low­ing figure from one of the first pa­pers to for­mu­late the idea.

Figure: “Mean wave­length-de­pen­dent UV ab­sorbance co­effi­cients, av­er­aged over pub­lished mea­sure­ments for eight com­mon pro­teins”

In essence, pro­tein can block far-UVC light so that it does not reach DNA. Mam­malian cells tend to be 10-25 μm in di­ame­ter, while bac­te­ria tend to be 1 μm and viruses even smaller. Be­cause of this size differ­ence, far-UVC light has to pass through more pro­tein be­fore it gets to a mam­malian nu­cleus, and ac­cordly it should be much weaker by the time it hits mam­malian DNA. In ad­di­tion, on most parts of the body, we are pro­tected by an outer ker­atin-rich (ker­atin is a pro­tein) layer 10-40 μm thick called the stra­tum corneum. Cells in the stra­tum corneum are some­where philo­soph­i­cally be­tween dead and al­ive—they main­tain home­osta­sis and com­plex in­ter­cel­lu­lar en­vi­ron­ments, but they lack DNA, so they are safe from can­cer. Be­cause it passes first through the pro­tein-rich stra­tum corneum, far-UVC light should be greatly at­ten­u­ated be­fore it even reaches the cell mem­branes of vuln­er­a­ble cells.

Of course, if we’re go­ing to be us­ing far-UVC light around hu­mans, we need more than just a bio­phys­i­cal ar­gu­ment. We also need em­piri­cal ev­i­dence. So what does the em­piri­cal ev­i­dence sug­gest about safety? The Na­ture ar­ti­cle cites three stud­ies that ex­per­i­mented with far-UVC light on hu­man cells, on lab grown hu­man skin, and on live mice. Th­ese stud­ies show promise for far-UVC as a safe ger­mi­cide, but they’re far from fully es­tab­lish­ing safety.

Safety Con­cerns for Individuals

What hap­pens to a per­son who has been re­peat­edly ir­ra­di­ated by far-UVC light? What are the health risks? What do we know? What don’t we know?

Cancer

UV light is fa­mously car­cino­genic, so can­cer is a cen­tral con­cern when it comes to as­sess­ing far-UVC’s safety. Ac­cord­ingly, the three safety pa­pers mainly seek to as­sess can­cer risk. Of course, can­cer can be slow to de­velop, so it isn’t pos­si­ble to ir­ra­di­ate test sub­jects and count can­cer cases within a rea­son­able timeframe. In­stead, can­cer must be in­di­rectly as­sessed.

Cancer is caused by ge­netic mu­ta­tions—we’re as cer­tain about that as we are about any­thing in hu­man biol­ogy—so by mea­sur­ing DNA dam­age you can get some sort of mea­sure of car­cino­genic­ity.

So that’s what the au­thors did. They mea­sured DNA dam­age un­der 207 nm light in lab grown hu­man skin in vitro, un­der 207 nm light in mice in vivo, and ex­panded their re­sults to 222 nm light on both hu­man skin and mice. Their re­sults were cer­tainly promis­ing, but the work is far from suffi­cient for fully demon­strat­ing can­cer safety.

There are two sep­a­rate mechanisms for DNA dam­age from UV light, and the safety stud­ies re­ally only ad­dress one of the two mechanisms. We’ll dis­cuss them sep­a­rately:

Direct DNA damage

Direct DNA dam­age oc­curs when pho­tons are ab­sorbed by DNA. The ex­cited DNA breaks the bonds be­tween the nu­cleotide bases, and the bonds can re­form with ad­ja­cent bases in­stead of op­po­site bases, dis­rupt­ing the dou­ble he­lix struc­ture in a type of le­sion called a pyrim­i­dine dimer.

UVB and UVC light can both in­ter­act di­rectly with DNA in this way. This is the mechanism for UVC’s ger­mi­ci­dal ac­tion, but at lower in­ten­si­ties, in­stead of lethal DNA de­struc­tion, le­sions can turn into mu­ta­tions. The body re­acts to this kind of dam­age by kil­ling and shed­ding dam­aged skin cells in the form of sun­burn.

I feel pretty con­fi­dent that this kind of dam­age does not hap­pen in mam­malian skin from far-UVC light. First, the ba­sic bio­phys­i­cal ar­gu­ment is strong. Few pho­tons should reach the nu­cleus (and num­ber of pho­tons should ba­si­cally de­ter­mine num­ber of le­sions). The light needs to pass through the ker­atin-rich (and there­fore far-UVC ab­sorb­ing) stra­tum corneum be­fore even reach­ing the rele­vant parts of the epi­der­mis.

The em­piri­cal ev­i­dence is also com­pel­ling. Ex­per­i­men­tally, in vitro, as ex­pected, ir­ra­di­at­ing lab-grown hu­man skin with stan­dard ger­mi­ci­dal UVC light caused a huge num­ber of pyrim­i­dine dimers—stan­dard ger­mi­ci­dal UVC light is highly car­cino­genic. Ir­ra­di­at­ing the hu­man skin model with far-UVC, how­ever, caused no statis­ti­cally sig­nifi­cant in­crease in these types of DNA le­sions:

Figure: In­duced yield of two types of pyrim­i­dine dimers, from fluences of stan­dard ger­mi­ci­dal UVC and from far-UVC light.

Ad­di­tion­ally, in live mice, there was no ev­i­dence of sun­burn in mice ex­posed to far-UVC—sug­gest­ing that di­rect DNA dam­age must be min­i­mal. The skin of unir­ra­di­ated mice and the skin of mice ir­ra­di­ated with far-UVC looked the same, while in mice ir­ra­di­ated with stan­dard ger­mi­ci­dal UVC, the skin was visi­bly al­tered and had a thick­ened epi­der­mis.

Figure: A.) Rep­re­sen­ta­tive cross-sec­tional images of mouse skin. B.) Aver­age epi­der­mal thick­ness for non-ir­ra­di­ated mice, mice un­der stan­dard ger­mi­ci­dal UVC, and mice un­der 207 nm UVC.

Indi­rect DNA damage

Indi­rect DNA dam­age oc­curs when pho­tons are ab­sorbed by other molecules in the cell, and these molecules re­act to form free rad­i­cals and other re­ac­tive species, which in turn re­act with (other molecules which re­act with other molecules … which re­act with) DNA, caus­ing mu­ta­tions via an ox­ida­tive stress mechanism. UVA, UVB, and UVC light can all cause in­di­rect DNA dam­age. This kind of dam­age causes skin can­cer, but im­por­tantly it does not ac­ti­vate the same defenses as di­rect DNA dam­age—no sun­burn.

The bio­phys­i­cal rea­son­ing that sug­gests that far-UVC doesn’t cause di­rect DNA dam­age doesn’t ap­ply neatly for in­di­rect dam­age: Far-UVC is quickly at­ten­u­ated in the outer layer of the skin, but how far can re­ac­tive chem­i­cal species formed near the sur­face prop­a­gate? Could they make their way down to vuln­er­a­ble cells in the epi­der­mis? As far as I can tell, the an­swer to this ques­tion is un­known. Indi­rect DNA dam­age is only rel­a­tively re­cently un­der­stood, com­pletely un­rec­og­nized in 1980 and re­main­ing some­what con­tro­ver­sial up through the early 2000’s—it wasn’t un­til 2009 that the WHO rec­og­nized tan­ning beds as a definite can­cer risk—so there’s still a lot of un­cer­tainty. What is known is that in gen­eral, chem­i­cals can diffuse through the skin, and some of the chem­i­cal species we’re wor­ried about are sta­ble in the body. More re­search is needed to rule out this pos­si­bil­ity.

In ad­di­tion, the em­piri­cal ev­i­dence for far-UVC’s safety from di­rect DNA dam­age does not ap­ply to in­di­rect DNA dam­age. The mouse’s lack of sun­burn in the in vivo study is mean­ingless as in­di­rect DNA dam­age does not cause sun­burn. The le­sions they look for, pyrim­i­dine dimers, are spe­cific to di­rect in­ter­ac­tions be­tween pho­tons and DNA. Indi­rect DNA dam­age causes differ­ent le­sions.

Cancer Safety Conclusion

Although the re­sults are promis­ing, can­cer safety has not been fully es­tab­lished. Direct DNA dam­age is min­i­mal, but in­di­rect DNA dam­age is a huge open ques­tion.

Non-can­cer cell damage

Another po­ten­tial point for con­cern is non-can­cer cell death. The in vitro study found that sig­nifi­cant fluences of 207 nm light kill 80% of ex­posed hu­man fibro­plasts (der­mis cells):

Is this con­cern­ing? Maybe not. Ex­cept on mu­cous mem­branes and open wounds, ex­posed cells will be dead-ish (part of the stra­tum corneum) to be­gin with. Still, more in­ves­ti­ga­tion is needed: Is it okay to re­peat­edly de­stroy the sur­face layer of cells on our eyes? It may not be a prob­lem, but I’d want at least a cou­ple ex­pert opinions if not a safety study be­fore ex­pos­ing my eyes to some­thing like that.

And the fibro­plast cell death also raises the ques­tion: What is kil­ling the cells? The au­thors kind of gloss over this point—they cite an­other pa­per and say it’s prob­a­bly mostly cell mem­brane dam­age. Be­fore far-UVC is widely im­ple­mented, we need to be more con­fi­dent that it is in fact cell mem­brane dam­age and not some­thing more ne­far­i­ous.

Limited Scope of Safety Studies

It’s also im­por­tant to note the rea­son why the safety stud­ies were con­ducted: The au­thors en­vi­sioned us­ing far-UVC to fight an­tibiotic-re­sis­tant bac­te­rial in­fec­tions dur­ing surgery. They thus as­sumed a sur­gi­cal en­vi­ron­ment, which means that ap­pli­ca­bil­ity to pub­lic spaces is limited:

The mouth is cov­ered by a face mask in surgery. Safety has not been es­tab­lished for the parts of the in­side of the mouth that don’t have the stra­tum corneum. If we’re all wear­ing face masks, then this isn’t a prob­lem, but if we’re imag­in­ing far-UVC light can let things go back to “nor­mal,” then we need to think about the safety of our mouths. The in­sides of our mouths of course won’t be as ex­posed as our skin (the ex­act level of ex­po­sure de­pends on the po­si­tion­ing of the ger­mi­ci­dal lamp, the re­flec­tivity of sur­faces, and the tics and fa­cial pos­ture of the per­son in ques­tion), but they will be ex­posed enough that we should know more about far-UVC’s can­cer risk on mu­cous mem­branes.

And what about ex­posed wounds? Once again, safety has not been es­tab­lished for cells not cov­ered by the stra­tum corneum. In the sur­gi­cal en­vi­ron­ment, the nurses and doc­tors will not have ex­posed wounds. The pa­tient’s de­creased risk of sur­gi­cal site in­fec­tion is likely worth the un­known risks of far-UVC light on ex­posed flesh. But what if I’m walk­ing around in pub­lic spaces with a skinned knee?

Fi­nally, the safety stud­ies fo­cus en­tirely on mam­mals. In the sur­gi­cal en­vi­ron­ment, hu­mans are the only rele­vant en­tities that need to be pro­tected. Many pub­lic spaces are open to pets, live­stock, and ur­ban wildlife. Even if you only rec­og­nize the value of an­i­mals’ lives with re­spect to what they can do for hu­mans, many peo­ple keep rep­tiles or birds that they love, many peo­ple eat birds and fish and in­sects, and we rely on var­i­ous or­ganisms from across the an­i­mal king­dom for ecosys­tem sta­bil­ity. We should prob­a­bly try to avoid caus­ing a skin can­cer epi­demic in non-mam­malian clades.

Com­mu­nity-level Concerns

Even if far-UVC is com­pletely safe for hu­mans and other macro­scopic or­ganisms, the po­ten­tial for wide­spread use of far-UVC leads to a num­ber of other con­cerns that need to be ad­dressed be­fore such a solu­tion is im­ple­mented.

Ac­quired Resistance

In gen­eral, ger­mi­cides should be used con­ser­va­tively be­cause of the po­ten­tial for ac­quired re­sis­tance. Medicine is an evolu­tion­ary race to nowhere, with pathogens evolv­ing to sur­vive what­ever we use to fight them. UVC light is no ex­cep­tion. As dis­cussed in a liter­a­ture re­view, one re­search group man­aged to teach E. coli to bet­ter sur­vive UVC ir­ra­di­a­tion.

In the case of the lab-cre­ated E. coli ac­quired re­sis­tance, the de­gree of re­sis­tance was fairly weak. Lethal doses of light were still very pos­si­ble. It’s not cur­rently known whether or not full re­sis­tance by microor­ganisms is pos­si­ble or likely. More ex­per­i­men­ta­tion will offer fu­ture sci­en­tists a clearer pic­ture.

In the mean­time, we should re­serve UVC light for cases with high po­ten­tial benefit and lower po­ten­tial for ac­quired re­sis­tance. Ubiquitous use of far-UVC light in pub­lic spaces has the po­ten­tial to teach re­sis­tance to all fu­ture pathogens, so that when the next epi­demic or pan­demic comes along, we’ll be com­pletely neutered.

Is a More Ster­ile World a Healthier World?

UVC light kills more than just pathogens. It kills all microor­ganisms in­dis­crim­i­nately. We don’t know what would hap­pen if we kil­led all bac­te­ria in our pub­lic spaces. It could lead to prob­lems. Bac­te­ria play an im­por­tant role in a lot of ecolog­i­cal pro­cesses like the de­com­po­si­tion of or­ganic waste. And if it turns out that it is a bad idea to de­stroy all microor­ganisms in our pub­lic spaces, it’s not nec­es­sar­ily some­thing we can come back from. An es­tab­lished colony of benefi­cial or harm­less bac­te­ria can pro­tect against the growth of harm­ful bac­te­ria. If you kill your gut bac­te­ria with an­tibiotics you risk get­ting a harm­ful new micro­biome. Could the same be true at a gro­cery store?

The Law of Un­in­tended Consequences

Even if we can es­tab­lish safety for the con­cerns I’ve raised above, we can never be sure that we’ve thought of ev­ery­thing that can go wrong. In en­vi­ron­men­tal­ism we rec­og­nize the “Law of Un­in­tended Con­se­quences:” We are very very far from un­der­stand­ing the world perfectly, so big tech­nolog­i­cal shifts will always have un­fore­seen effects.

Of course, the law of un­in­tended con­se­quences is not a rea­son to hold back on change en­tirely. We can never know the con­se­quences of our ac­tions fully, so if we always avoided act­ing on un­cer­tainty, we would never do any­thing at all. But it is pos­si­ble to miti­gate the po­ten­tial ad­verse effects. In gen­eral, it is bet­ter to roll out some­thing like this in a smaller en­vi­ron­ment where it has high po­ten­tial to help (like in sur­gi­cal rooms). Safety re­sults can be as­sessed in those small en­vi­ron­ments be­fore we ex­pose the pub­lic at large.

The Stick­i­ness of So­cial Change

Every­thing I’ve said so far is a con­cern, but des­per­ate times call for des­per­ate mea­sures. Could the use of far-UVC be worth it, if limited to the worst of the COVID pan­demic? This is the wrong ques­tion. We need to ask: If we start us­ing far-UVC in pub­lic spaces dur­ing the pan­demic, re­al­is­ti­cally, will we stop us­ing it when the pan­demic is over? Things like this tend to have stay­ing power.

This po­ten­tial for stay­ing power is es­pe­cially dan­ger­ous when paired with the pre­ced­ing three con­cerns. The risk of ac­quired re­sis­tance in­creases with use, and we don’t have laws that pre­vent mi­suse—when far-UVC as a safe ger­mi­cide be­comes more ac­cepted, it may, like an­tibiotics, be adopted by fac­tory farms, in­creas­ing even more the prob­a­bil­ity of new re­sis­tant pathogens.

Killing all microbes in pub­lic spaces for a longer pe­riod of time may have worse con­se­quences than limited use dur­ing a pan­demic. Scien­tific un­der­stand­ing of the micro­biome is still pretty young, but we do know that these benefi­cial microbes are ex­changed be­tween in­di­vi­d­u­als. Ubiquitous far-UVC light would end micro­biome ex­change in pub­lic set­tings. As far as I can tell, we have no idea what the con­se­quences of this might be.

We don’t know what the un­in­tended con­se­quences of in­tro­duc­ing far-UVC light to pub­lic spaces might be, but we do know that the dis­cov­ery of nega­tive con­se­quences of­ten doesn’t end the use of a new tech­nol­ogy. For ex­am­ple, in the 1970’s and ’80’s, it was as­sumed that UVA light was safe. UVA does not cause di­rect DNA dam­age, and in­di­rect dam­age was not yet dis­cov­ered. Ac­cord­ingly, start­ing in the late ’70’s, tan­ning sa­lons that ir­ra­di­ated users with UVA light (caus­ing a “safe” tan with­out a sun­burn) opened up all across Europe and the US. We now have known for more than 10 years that UVA light causes can­cer. And tan­ning beds are still around! In most of the US, tan­ning beds are not only com­pletely le­gal, but also ac­cessible to minors. One study found that hun­dreds of thou­sands of skin can­cer cases per year are as­so­ci­ated with the use of tan­ning beds (they did not give an es­ti­mate of how many of these cases end up be­ing fatal). In­cor­rectly stat­ing that a tech­nol­ogy is safe can lead to huge num­bers of pre­ventable deaths, even af­ter the mis­take has been cor­rected.

I don’t want to have a lengthy dis­cus­sion of ethics here. This post is in­tended to be more an anal­y­sis of safety and po­ten­tial nega­tive con­se­quences. Still I need to at least bring it up:

What about hu­man rights? Is it okay to ir­ra­di­ate peo­ple with­out their con­sent? How do you ob­tain mean­ingful con­sent for some­thing like this?

Of course, we ir­ra­di­ate peo­ple with­out their con­sent all the time with ra­dio and wifi and cell phones, but those are lower en­ergy waves far far less likely to be dan­ger­ous. Far-UVC, even if it is non-car­cino­genic and doesn’t pen­e­trate the stra­tum corneum, does definitely af­fect our bod­ies: It kills our skin micro­biome. Just go­ing off of my gut in­stinct, I’m eth­i­cally fine with wifi, while far-UVC,in a hy­po­thet­i­cal fu­ture where safety is more es­tab­lished, seems much more eth­i­cally ques­tion­able.

In the US, we put fluoride in our wa­ter. If you don’t want to drink fluoride you have to sig­nifi­cantly in­con­ve­nience your­self to avoid it. Eth­i­cally, does our ap­proach to fluoride work for far-UVC? In the US, we don’t vac­ci­nate peo­ple with­out con­sent, even though the un­vac­ci­nated dam­age herd im­mu­nity. We don’t put vac­cines in the wa­ter. Is far-UVC in pub­lic spaces more like fluoride or more like vac­cines?

Conclusion

I know I’ve seemed very nega­tive about far-UVC for the past three thou­sand words, but I ac­tu­ally am very ex­cited about its po­ten­tial. It is be­cause it is ex­cit­ing that I think this kind of safety in­ves­ti­ga­tion is nec­es­sary.

We should not be us­ing far-UVC as a ger­mi­cide in pub­lic spaces any time soon. A bet­ter goal might be smaller-scale im­ple­men­ta­tion within med­i­cal wards to pre­vent hos­pi­tal spread of coro­n­avirus or other con­ta­gious ill­nesses, but we’re still a long way off from even that. There are a lot of hur­dles far-UVC still needs to clear be­fore we de­cide it is safe. It may well clear those hur­dles. I hope it does.

Should in­ves­ti­ga­tions into far-UVC be con­tinued? Ab­solutely. Should the in­ves­ti­ga­tions be ex­panded? As some­one who is not broadly knowl­edge­able about the fron­tiers of medicine, I have no idea whether far-UVC is be­ing ne­glected rel­a­tive to other promis­ing tech­nolo­gies at similar stages of de­vel­op­ment. Still, the coro­n­avirus pan­demic has demon­strated the life-sav­ing value of this kind of re­search. Public fund­ing into this kind of re­search should be ex­panded in gen­eral, so that by the time the next pan­demic hits we can know bet­ter what tech­nolo­gies are safe and effec­tive.

Main Sources

In­spira­tions

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

Roko Mijic, Alexey Turchin. Ubiquitous Far-Ul­travi­o­let Light Could Con­trol the Spread of Covid-19 and Other Pan­demics. LessWrong. March 2020.

Safety

Buo­nanno, M. et al. 207-nm UV light—a promis­ing tool for safe low-cost re­duc­tion of sur­gi­cal site in­fec­tions. I: in vitro stud­ies. PLoS One 8, e76968 (2013).

Buo­nanno, M. et al. 207-nm UV Light-A Promis­ing Tool for Safe Low-Cost Re­duc­tion of Sur­gi­cal Site In­fec­tions. II: In-Vivo Safety Stud­ies. PLoS One 11, e0138418 (2016).

Buo­nanno, M. et al. Ger­mi­ci­dal Effi­cacy and Mam­malian Skin Safety of 222-nm UV Light. Ra­diat. Res. 187, 483–491 (2017).

Ger­mi­ci­dal UVC Liter­a­ture Review

Dai T.H., Vra­has M.S., Mur­ray C.K., Ham­blin M.R. Ul­travi­o­let C ir­ra­di­a­tion: an al­ter­na­tive an­timicro­bial ap­proach to lo­cal­ized in­fec­tions? Ex­pert Rev. Anti In­fect. Ther. 2012;10:185–195.