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Views expressed in this article are my own and do not necessarily reflect those of my employer SecureBio.

Summary

  • Far-UVC has great promise, but a lot of work still needs to be done
    • There still are many important open research questions that need to be answered before the technology can become widely adopted
    • Right now, a key priority is to grow the research field and improve coordination
  • The main reason far-UVC is so promising is that widespread installation could passively suppress future pandemics before we even learn that an outbreak has occurred 
  • Higher doses mean more rapid inactivation of airborne pathogens but also more risk for harm to skin, eyes, and through indoor air chemistry. Therefore, the important question in safety is, “How high can far-UVC doses go while maintaining a reasonable risk profile?
  • Existing evidence for skin safety within current exposure guidelines seems pretty robust, and I expect that skin safety won't be the bottleneck for far-UVC deployment at higher doses.
  • Current evidence around eye safety is much more sparse than for skin safety. Eye safety seems like it could be the bottleneck to what doses of far-UVC can be reasonably used. 
  • Undoubtedly, far-UVC has a substantial impact on indoor air chemistry by producing ozone, which oxidizes volatile organic compounds in the air that can result in harmful products such as particulate matter.
    • Little research has been done on methods to mitigate this issue. 
    • This might turn out to be a bottleneck to what doses of far-UVC can be reasonably used, but I am really uncertain here.
  • There is no doubt that far-UVC can dramatically reduce the amount of airborne pathogens within a room (inactivation of ~98% of aerosolized bacteria within 5 minutes). Crucially, we don't know how well this translates into an actual reduction in the total number of infections.
  • Very few people have thought about how the adoption of far-UVC could be driven and what a widespread deployment of the technology could look like
  • So far, there is little to no regulation of far-UVC. 
    • In the US, (potential) regulation of far-UVC seems quite messy, as no authority has clear jurisdiction over it.

Introduction

Far-UVC (200-235 nm) has received quite a bit of attention in EA-adjacent biosecurity circles as a technology to reduce indoor airborne disease spread and is often discussed in the context of indoor air quality (IAQ). Notably, Will MacAskill mentioned it often throughout various media appearances in 2022. 

I have been working on research around far-UVC for the past 8 months. More specifically, we wrote an extensive literature review on skin and eye safety (EDIT: now published online [open access] submitted & soon™ to be published as an academic paper). We also coordinated with many researchers in the field to lay out a plan for the studies that still need to be done to get a more comprehensive understanding of the technology’s safety & efficacy. 

Although far-UVC has been discussed on the forum, the existing information is relatively shallow, and most in-depth knowledge is either buried in technical research papers or not publicly available since a lot of intricacies are mostly discussed informally within the research community.

In this post, I will first offer high-level thoughts and then go over different categories of information around far-UVC (safety, efficacy, indoor air chemistry, adoption, and regulation) to provide my current perspectives & takes. Please note that I am much more familiar with safety aspects than with the other categories. Also, this is not a general overview of far-UVC, what it is, and how it works. For a relatively recent and comprehensive introduction, I recommend “Far UV-C radiation: An emerging tool for pandemic control”. 

High-level thoughts

  • Far-UVC seems like the only technology we currently know of that has the potential to passively mitigate a future catastrophic pandemic before we even know it is happening.
    • This is the main reason why it is so promising
    • For most of our other defenses against pandemics, e.g., masking/vaccines, we first need to notice a disease outbreak is occurring and then decide to deploy these countermeasures. 
    • Widespread far-UVC could potentially halt an outbreak at an early stage without us ever learning that it happened.
    • While upper-room germicidal UV (GUV), ventilation/filtration and portable air purifiers similarly work in a passive manner, they don't nearly reach the rates of rapid pathogen inactivation that far-UVC can.
      • There are also preliminary discussions about triethylene glycol and microwave inactivation as further passive interventions for controlling indoor airborne transmission but there is much less evidence for these. 
  • In contrast to conventional GUV systems installed in the upper-room or air purifiers, far-UVC works through whole-room direct exposure. This means that far-UVC could provide immediate disinfection of aerosols within people’s breath plumes. Plausibly, it could therefore help to slow down close-contact transmission, e.g. between people in a conversation. 
    • Whether this works in practice remains to be determined. 
  • Far-UVC is still a young technology and research field.
    • A lot remains to be done before it can become widespread.
    • For example, the first-ever conference on far-UVC only happened this June.
    • A far-UVC fixture currently costs ~$1000; the cheapest ones cost ~$500. There are approx. 20 (small) vendors of far-UVC fixtures.
  • Multiple EA(-adjacent) organizations are doing work around far-UVC; these are the ones I am aware of (there might be more):
  • The ultimate goal for far-UVC is to have it become ubiquitous in indoor spaces where a lot of transmission tends to occur (e.g., hospitals, public transport). 
    • From a biosecurity perspective, we only really care about far-UVC if we can achieve widespread adoption of cheap, safe & effective far-UVC. If we think that only marginal improvements to the current technology can be achieved, then it is not worth it to put substantial resources into far-UVC. 
  • A lot of information propagation in the far-UVC field happens informally via regular Zoom meetings or email lists. Many of the key researchers have known each other for a long time. 
    • This is probably normal, especially for smaller fields.
  • “Far-UVC” is often used almost synonymously with 222 nm since KrCl lamps with a peak emission wavelength at 222 nm have been the most efficient far-UVC sources available. Due to this, most far-UVC research has focused on 222 nm.  
    • We should be open-minded about deploying other wavelengths in the far-UVC range when other efficient sources become available.
    • There is an open question about what wavelengths would be ideal for air disinfection.
    • For example, there is a case that slightly longer far-UVC wavelengths (~230 nm) could be superior to 222 nm.
      • This is because the solid-state emitter tech development for ~230 nm seems more promising. You would also get less ozone production and increased penetration through media like bigger saliva droplets.
    • Multi-wavelength systems might be promising as well.

Safety

  • Before far-UVC can become widely used, we need to understand how safe it is at what doses
    • Higher doses means more rapid inactivation of airborne pathogens but also more risk for harm to skin, eyes and through indoor air chemistry
      • Presumably, achieving rapid enough inactivation to achieve a reduction in close contact transmission would require significantly higher doses than what current guidelines permit
    • Therefore, the important question in safety is, “How high can far-UVC doses go while maintaining a reasonable risk profile?
  • We have compiled a Google Sheet that lists the results of most of the important far-UVC safety studies. It gives a good overview but is not comprehensive, as you can see from the (potentially relevant) studies linked at the bottom that haven't been added yet. Note the readme in the top left and let me know if you spot any mistakes.
  • Existing evidence for skin safety within current exposure guidelines seems pretty robust.
    • Even at much higher doses than current guidelines permit, there is preliminary evidence that skin safety isn't a significant issue (at least for healthy adults)
    • I expect that skin safety won't be the bottleneck for far-UVC deployment at higher doses
  • Current evidence around eye safety is much more sparse than for skin safety
    • Studying the eyes is much harder, for example, due to the dynamic nature of the eye (blinking + tear film)
      • You also can't easily take biopsies of the eye like you can do with the skin
      • Designing useful eye safety trials is difficult and experienced ophthalmologists we have spoken to are skeptical of many study proposals that have been put forward. 
    • There is some solid evidence of eye safety from studies on rodents, most notably from Kaidzu et al. (2019; 2021; 2022).
    • Due to shielding by the eye socket and lids, the eye receives a much lower dose of far-UVC in typical overhead deployment scenarios than the skin.
      • Nonetheless, eye safety seems like it could be the bottleneck to what doses of far-UVC can be reasonably used
      • There seems to have been a near consensus in the field that eye safety hinges on how much protection the tear film offers. There is currently a lot of discussion and research ongoing about this question. 
      • The tear film contains a bunch of proteins and lipids that strongly absorb far-UVC, so some researchers assumed that the tear film could provide very strong protection, as it’s replenished with every blink.
        • The idea that the tear film offers nearly total protection against far-UVC photons is so widespread that even the CDC website says (as of 2023-07-07): “This increase was in response to data showing 222 nm energy does not penetrate the tear layer of the eye”
        • Recent (still unpublished) results cast doubt on this and the evidence suggests that the tear film provides almost no protection
        • One way to think about this is to compare the tear film with the stratum corneum, the outermost layer of the skin. At 222 nm, >90% of photons are absorbed in the approx. 16 µm thick stratum corneum, which is made up of dead cells that are almost entirely filled with proteins. These proteins are responsible for absorbing the far-UVC photons. The tear film, on the other hand, is only ~3-5 µm thick and mostly water, with some proteins and lipids in there. Accordingly, it shouldn't come as a surprise that the tear film attenuates nothing close to 90% of far-UVC photons.
    • Most research on far-UVC eye safety has focused on the cornea. The conjunctiva (and its goblet cells) have been studied much less. 
      • Also, the cornea and conjunctiva are very tightly innervated and full of little nerves
        • Maybe higher doses of far-UVC could induce unpleasant sensations by interacting with these nerves
      • Ultimately we care about whether higher doses of far-UVC could have some effect on vision (acuity, contrast sensitivity)

Efficacy

  • There is no doubt that far-UVC can dramatically reduce the amount of airborne pathogens within a room (inactivation of ~98% of aerosolized bacteria within 5 minutes (Eadie et al. 2022))
    • Crucially, we don't know how well this translates into an actual reduction in total number of infections.
      • Of course, on priors, you would expect a reduction in the number of airborne pathogens to result in reduced infection risk. Yet the real world is messy and a lot could depend on air circulation in the specific environment, transmissibility of the pathogen, susceptibility of people etc. 
    • What is needed is a well-powered, carefully controlled real-world trial of far-UVC that uses the number of infections as the primary outcome. Many researchers in the field agree with this need.
      • Only one such trial is currently ongoing, but more needs to be done
      • Unfortunately, epidemiological studies are 1) very expensive and 2) very hard to do well
      • We have a study proposal for a trial on offshore oil platforms (Message me if you know anyone working for an oil company or have a few million dollars to spare)
  • We believe that demonstrating efficacy in a real-world environment would be crucial to make more people excited about the promise of far-UVC and drive adoption in the future.
    • It will be important that the first epidemiological studies are carefully controlled so that any effect of far-UVC can be clearly observed 
    • The first real-world trials showing ambiguous results because of lackluster study design would probably be bad for far-UVC adoption
      • People worry about this because it seems likely that this is what happened with epidemiological studies of upper-room GUV in the 1940s and 1950s
        • The first epidemiological trials of upper-room GUV showed great results but subsequent similar trials were more ambiguous
          • The design of trials that showed more ambiguous results has been criticized. While upper-room GUV was installed in school classrooms, the kids shared other indoor environments (e.g. the schoolbus) that weren't equipped with upper-room GUV. Presumably, infections just shifted away from classrooms to these other shared environments. 
        • It seems likely that this made people somewhat disillusioned with the technology and is part of the reason why upper-room GUV hasn't been more popular
  • The development of standardized test methods for evaluating germicidal efficacy will be necessary for comparing different products and determining reasonable performance expectations in complex, real-world environments.

Indoor air chemistry

  • Throughout 2023, the most hotly debated topic within the far-UVC field has been the impact of far-UVC on indoor air chemistry
    • This doc links to most (all?) relevant studies that have been published on this issue: http://bit.ly/guv-chem 
  • Undoubtedly, far-UVC has a substantial impact on indoor air chemistry by producing ozone, which oxidizes volatile organic compounds in the air that can result in harmful products such as particulate matter
    • The debate surrounds the question of how detrimental this is and existing studies seem to disagree somewhat to what extent this is a substantial issue
    • Importantly, little research has been done on methods to mitigate this issue. 
      • For example, using activated carbon filters to remove ozone, making sure far-UVC is used with sufficient ventilation to remove ozone or altering far-UVC fixture designs. 
  • A lot of research here is ongoing and the issue is far from settled
  • This might turn out to be the bottleneck to what doses of far-UVC can be reasonably used, but I am really uncertain here.
    • This hinges on what future research uncovers about mitigation strategies for this issue

Adoption (real-world deployment)

  • Very few people have thought about how adoption of far-UVC could be driven and what a widespread deployment of the technology could look like
    • Presumably, the vendors of far-UVC fixtures have business plans about how to increase demand, but they aren't approaching this question from a pandemic-preparedness perspective
    • One interesting deployment mode would be far-UVC fixtures with two modes: “business as usual” mode and “emergency” mode
      • In non-pandemic times, you would have the lamps running at exposure levels that pose a negligible or acceptable risk for the vast majority of the population
      • Once a pandemic threat is detected and infections are ramping up, the risk-benefit calculus changes and you could flip the switch to emergency mode for the lamps to run at substantially higher exposure levels
        • Ideally, these emergency mode doses would be sufficient to reduce the transmission of a pathogen with measles-level infectivity below an R0 of 1
          • While there are some intuitions about this, we don't really know what exposure doses would be needed to achieve this. It would be great to see more modeling work done around this question.
        • If it turns out that these higher doses are still reasonably safe for the skin, but pose a greater risk to the eyes, you could mandate wearing safety goggles in places where the far-UVC fixtures are running—just like masks were mandated during Covid. 
          • In a severe bioterrorist attack, this could be a reasonable tradeoff
      • This would be great because you wouldn't need to go through the laborious retrofitting of buildings with e.g. better ventilation/filtration. Flipping a switch is much more simple. 
      • Of course, far-UVC manufacturers aren't currently incentivized to do this. Why would you install a more powerful source (presumably at a higher cost), if that power isn't usually needed?
        • On the other hand, I have heard that the sources in current far-UVC fixtures are already run at lower power to comply with exposure guidelines. 
    • You could also imagine that far-UVC fixture designs incorporate ways to adapt the irradiance based on what is happening in the room. E.g., via monitoring noise and low-resolution infrared cameras.
      • E.g., a lower irradiance is deployed if few people are in the room and no one is talking, but as soon as people move more closely together and start a conversation, the irradiance could be increased.
  • Trying to get a decent cost-benefit analysis for the widespread adoption of far-UVC seems worthwhile 
    • Including risks from ozone, volatile organic compounds, particulate matter, etc.
    • Also, modeling how useful far-UVC would be under different pandemic scenarios
    • I am not aware of any decently comprehensive cost-benefit analysis

Regulation

  • So far, there is little to no regulation of far-UVC. 
    • There are broadly accepted exposure “guidelines”, but these are not standards (at least in the US). 
    • Exposure guidelines in the US are set by the American Conference of Governmental Industrial Hygienists (ACGIH). 
      • ACGIH exposure guidelines for far-UVC were updated in 2022 and are substantially higher than in the rest of the world, where those of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) apply.
  • Another important player on the regulation side of far-UVC is the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE)
    • ASHRAE develops technical standards (“building codes”) that are very widely adopted and indicate things like the minimal amount of air changes per hour a building should have
      • These are frequently turned into legislation by policymakers
    • They recently developed a new standard on indoor pathogen mitigation (Standard 241P, Control of Infectious Aerosols). 
      • The standard was recently released. It doesn't mention far-UVC explicitly but talks about GUV in a few places. 
      • Interestingly, the standard defines “the amount of equivalent clean airflow necessary to substantially reduce the risk of disease transmission during infection risk management mode.
        • AFAIK it is the first standard to use equivalent clean airflow (similar to equivalent air changes per hour) as the key metric. This is interesting because it is agnostic to what technology is used to achieve the necessary levels of equivalent clean airflow!
        • As mentioned above, far-UVC can achieve much higher rates of equivalent air changes per hour than other technologies.
        • Accordingly, the standard might incentivize more use of far-UVC
      • (I have only skimmed this standard, and my interpretation might be misguided)
  • In the US, (potential) regulation of far-UVC seems quite messy, as no authority has clear jurisdiction over it.
    • If it is advertised as a medical device, the Food and Drug Administration would need to get involved
    • Since on a very broad definition it counts as a pesticide, the Environmental Protection Agency also has a word
    • The Centers for Disease Control and Prevention makes recommendations about disease transmission mitigation strategies and has recently started to mention far-UVC on their website
    • Since far-UVC might pose a risk to workers, the Occupational Safety and Health Administration could regulate it
  • I have heard that some of the US regulators noted above are becoming more interested in far-UVC. Clearer regulations/standards might emerge in the coming years. 
    • The White House is also interested in germicidal UV
      • A 2022 report by the White House Steering Committee for Pandemic Innovation of the National Science and Technology Council notes, “Expand the use of GUV in priority congregate settings through research, test and evaluation, real-world demonstration projects, clear standards and guidance, and LED technology innovation.”
      • There is also an ongoing White House challenge focused on clean air in buildings that mentions conventional GUV
      • Apparently, the development of the indoor pathogen mitigation standard by ASHRAE was also motivated by interactions between the White House and ASHRAE
  • Standards and regulations developed by trusted entities like ASHRAE and UL serve as critical enablers of far-UVC.
  • Far-UVC manufacturers desperately want to see standardization but don't want to face annoying regulations
    • They want standardization to gain trust and pull demand

Let me know if you have any questions! Also, feel free to DM me if you want to chat about far-UVC and working in the field. 

Big thanks to my colleague Lenni Justen with whom I arrived at many of these perspectives, and thanks to Vivian Belenky and Jasper Götting for valuable discussions and inputs.

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Your interpretation of Standard 241 is not misguided. I was one of the people who developed the standard; we designed it to be technology-agnostic and with UV in mind. It will incentivize UV, once the standards have been developed to say how much equivalent clean air a UV fixture provides. I suspect that in a few years when the tech matures, it will be one of the most cost-effective ways of meeting 241's requirements.

I've wondered about the interaction between far-UVC and immunity:

  • as well as protecting us against a scary novel pandemic-level pathogen, far-UVC would also kill off germs for various "common or garden" infections
  • at first glance, this sounds like a pretty great cherry on the cake
  • but could it exacerbate pandemic risk by reducing immunity, thereby making it easier for a bioweapon engineer to create a scary pathogen?

I was thinking along these same lines but for skin-microbiota... we are lagging behind understanding this compared to gut-microbiota but it seems like the diversity is pretty important to our overall health? Its probably only a risk worth considering for the "install it in all the offices" rather than against using far-UVC in pandemic situations, but I guess research would be needed to assess the risks for skin disorders, or whatever else these microbiota might be important for? 

That's likely an even smaller issue. Far-UV inactivates the transient microbiome on the upper skin surface but not in the pores where the majority of the bacteria live. It’s also strictly line of sight and the skin is pretty wrinkly and only small areas (e.g., back of the hands) are exposed and you constantly re-seed your microbiome from other parts of the body. There’s prelim data from hairless mice which found no changes to the microbiome.

I agree with Jasper and don't expect impacts on the skin microbiome to be a big deal, but it would, of course, be good to get some more data. 

One useful comparison is that healthcare workers use alcohol-based hand sanitizers many times a day, which are quite potent and can kill microbes in areas inaccessible to Far-UVC. 

In this review paper, they only saw changes to the composition of the skin microbiome after extremely frequent daily hand disinfection: 

“Overall microbe diversity on hands was unchanged with alcohol-based hand rub use or hand washing, with the exception that overall diversity was lower in those that reported >40 hand washing with soap and water events per shift”

From Edmonds-Wilson et al. 2015. I don't know how bad reduced diversity is and what harmful effects that might have. 

While these alcohol-based hand sanitizers are quite effective, they evaporate quickly and accordingly kill microbes in a very short time span. In certain scenarios, you could imagine far-UVC being different because it could kill off skin microbes at the back of your hands more or less continuously during the ~8 hours you are at work. This raises the question if this mode of continuous disinfection has different effects than the short bursts of frequent hand disinfection experienced by healthcare workers. I'd be surprised if the outcome is very different. 

Hi Sanjay, thanks for the comment!

sounds like a pretty great cherry on the cake

Indeed, I think part of the path to impact for far-UVC will be that adoption will hopefully be driven by, e.g., employers like Google equipping their offices with far-UVC lamps because they expect this to reduce the total number of sick days of their workers and therefore increase productivity + profits. Getting this type of evidence for efficacy would be great since it would be an excellent sales pitch to companies whose employees earn a lot, meaning sick days are costly. Ideally, you would be able to tell them something like, "Installing these far-UVC fixtures in the whole office will cost you $30,000, but based on existing evidence and our best models, you'll likely recoup those costs after approx. 18 months due to a reduction in sick days of your employees." 

Presumably, that would be a big boost for demand and competition, thereby reducing costs and increasing R&D. It could help to make far-UVC widespread enough to make a difference in stopping future outbreaks or slow down the spread of disease during the next pandemic. 

but could it exacerbate pandemic risk by reducing immunity, thereby making it easier for a bioweapon engineer to create a scary pathogen?

There has been very little research on the interaction of far-UVC and the immune system. It is a topic that often comes up in discussions around far-UVC safety and is related to the well-known "hygiene hypothesis," which says something like, "If you're not exposed to enough germs as a child, you might get more allergies." 

I want to see more research on this, but so far, it hasn't been as much of a priority. First, people wanted to figure out things like whether far-UVC could give you skin cancer or make you blind. By now, we know those things won't happen, so we can turn to more "second-order" type risks like immune system effects. 

However, I have a few intuitions about why this seems unlikely. First of all, it is an "end-game" worry in the sense that it seems like it would only become relevant once far-UVC is almost ubiquitous. Even if it becomes widespread, it would be installed in places like hospitals, shared offices, public transport, etc., but you probably wouldn't have it in your home or anywhere outside. Let's say you would spend ~10 h per day in environments that have much more sterile air than nowadays, but the other ~14 h, you're at home or wherever and still exposed to the germs of, e.g., your partner or children.  

Also, I expect that even widespread far-UVC wouldn't reduce fomite transmission much because its disinfection works by line of sight and is easily shielded. So your immune system would still be challenged by that type of transmission.

As I wrote in the post, we only really care about far-UVC if we can find a path to really widespread adoption and high enough doses to slow down or even stop the transmission of extremely infectious agents like measles. If we actually achieve pathogen suppression that strong, I find it hard to imagine a malevolent actor engineering a pathogen so scary that it overwhelms this system. Remember that far-UVC would only be one of our defenses against pandemics and would be combined with PPE, ventilation, medical countermeasures, etc.  

I also haven't seen any convincing evidence that a reduction in your exposure to germs dramatically worsens your immune system. While I haven't looked into it deeply, the hygiene hypothesis seems to be somewhat controversial and concerns things like allergies, not, e.g., doubling your susceptibility to common infections because of a worse immune system. 

Similarly, I have heard claims that due to all the social isolation, masking, etc., during the Covid pandemic, peoples' immune systems got worse. Yes, the flu + RSV season peaked earlier last winter and was decently bad, but I don't see how this can be attributed to a broad decrease in immune competency. Rather, it just seems like many people weren't exposed to these specific pathogens that they would have typically been challenged with more frequently. I'm not terribly knowledgeable here, so might be mistaken, would be curious if other folks have more insights.

The "hygiene hypothesis" is a complicated topic, so I'm not sure what the net balance would be:

  • cumulative RSV cases were, I believe, lower throughout the pandemic, even accounting for the later peak

  • common respiratory infections may not be so harmless, with e.g. flu recently being linked to increased risk of a bunch of diseases (https://www.cell.com/neuron/pdf/S0896-6273(22)01147-3.pdf), viruses anecdotally causing chronic illnesses such as ME/CFS and POTS (similar to Long Covid), and increasing evidence that many of these viruses actually persisting in the human body (like 12/22 MS patients having seasonal coronaviruses in their brain: https://pubmed.ncbi.nlm.nih.gov/1596089/) that can't be good.

  • similar viruses affect immunity towards each other. In some cases, this is helpful. A recent article found that people who remained asymptomatic with COVID were likely to have specific memory T cells from seasonal coronaviruses. On the other hand, this imprinting can go awry, when memory cells are ineffective against the new virus, and a broad antibody response to seasonal coronaviruses is actually a risk factor for Long Covid (and I believe severe covid as well) https://www.medrxiv.org/content/10.1101/2022.11.07.22282030v1.full-text

So I think this hygiene effect would be great for public health, but it might increase tail risk? Then again, the stronger hygiene there is, the harder it will be for (airborne) pandemics to occur, so I'd really expect it to be net positive.

Everything touched by the immune system is complicated, agree. But I strongly suspect the net balance will be highly positive, still:

a) As you wrote, seasonal respiratory disease is a massive problem, in the order of trillions of dollars of health and economic damage every year

b) There is some cross-reactivity, yes, but the tail events will be too different from what we usually have. Frequent common-cold exposure will not be the thing that protects us from a GCBR. Neither will the original antigenic sin play a role, as that usually requires quite closely related strains to matter. Overall, your immune system will be a bit less-well prepared for this particular pathogen family that you haven't encountered in a while, but that's also the case for any other sufficiently different pathogen. 

Just a couple of lay person observations to add here regarding the hygiene hypothesis:

  1. So far it seem hygiene interventions like hand washing, clean water, etc. have been net positive so based on this I think there is cause for optimism around more hygiene interventions. I think the scenario where decreasing infection is possibly harmful is in completely sterile environments but as others have pointed out, far-UVC seems unlikely to eliminate all pathogens we come into contact with. Also, I understand the hygiene hypothesis to be about increasing prevalence of allergies in cleaner environments but I remember reading that we are learning that only specific pathogens are responsible for reducing allergies and not that it is a lack of high levels of exposure to a wide array of diseases
  2. I think I have heard that certain infections can actually weaken your immune system. For example, Harvard Health says that avoiding infection is part of strengthening one's immune system. I am thinking (and experts have probably explored this) that perhaps one contributing factor to increased infection after lock downs was that covid had weakened people's immune systems.

Harvard Health says that avoiding infection is part of strengthening one's immune system

I was intrigued so looked at the link. It has heading "Healthy ways to strengthen your immune system" and says in one bullet point under this "Take steps to avoid infection, such as washing your hands frequently and cooking meats thoroughly", but doesn't say anything about why this would help strengthen the immune system (it just links to a page with steps for reducing infection risk). A possible alternative interpretation is that this is meant as advice for not getting sick rather than making the immune system more effective, and this seems more likely to me. But it's not clear.

Agreed - I wished I could learn more. In any case, I feel really uncertain about the hygiene hypothesis. Given that the advice to "collect bugs" for increased immunity is so widespread and even propagated by doctors it baffles me that it is so hard to find evidence for this advice. The advice also has serious bearing on people's well-being which is another reason that this claim should be investigated much more closely.

Thanks for this great post! Really fascinating!

Sorry if this was already asked, but I couldn't see it: how likely is it that pathogens would be able to develop resistance to UVC, and how quickly might that happen? If it did happen, how big a concern would it be? E.g. would it just be a return to the status quo, or would it be an overcorrection?

Excellent post. I love to see legible, reader-friendly summaries of high-level work on the forum. About time everyone updated their baseline knowledge on UVC.

Also, huge +1 to reaching out to Max expressing interest if anyone wants to work on this and feel that they bring something valuable to the table (even if something might not be available right away). I did this about six months ago and actually ended up contributing to a project. And what a great work experience it was overall!

Forgive me if this is a dumb question, but …  can't you just shine the light in places where it won't hit people?  A wash of light that passes over people's heads, between their cubicles, across vents and doors, but not shining directly on their skin and eyes?  Presumably with a dark absorber at the other end.  But it's light; it goes in straight lines.

This is not a dumb question; you have just described upper room uv, which is an established, successful, and worthwhile tech. But it requires skilled labor to install (to avoid accidentally getting the angle wrong and blasting people in the head) and it does not have as much potential upside as newer tech.

Great summary!

One thing I would like to add is that the field will need to find significant (>20x) cost reductions to deploy at a scale relevant to pandemic suppression. This seems very doable, if investments in R&D are made. What's the level of current & planned investments?

Also, I would expect the indoor chemistry issue to require decent ventilation/filtration at any relevant UVC intensity? This would unfortunately raise the cost and limit the flexibility of UVC

Re. cost reductions: That's a bit tricky. With the current lamp tech (KrCl excimer lamps), 20x is not on the table. Their cost floor is closer to 1/3 of the current cost. Next-gen (read: solid-state) emitters can achieve 20x in principle but are often still bottlenecked by fundamental academic research; we're eventually talking about ~5–10 years and 10s to 100s of M of $ to get to fab scale. There are two startups around a different promising approach that might be a bit faster but will require the same money. 

For any technologies that have a market, $100M of investment are doable, but far-UV faces a bit of a circular problem: Missing data (safety/effectiveness) → No official recommendations → No market → No emitter R&D and high product prices → Insufficient deployment that limits real-world data. There are now some market-shaping initiatives that will hopefully ameliorate this dynamic so that R&D money flows naturally. But as Max wrote, OP will hopefully also address some of those points after their RFI. 

Re. IAQ: The ozone/VOC data are still somewhat contested and in flux, so it remains to be seen what the far-UV impact on real-world IAQ will actually be. But you're generally right; it's best to view the IAQ interventions holistically. Ventilation/filtration can complement far-UV, and the best deployment scheme will depend on the environment. But I still don't worry too much about cost/flexibility limitations, as most environments in which far-UV would be first installed already have decent air handling systems (hospitals, airports, etc.)  

Thanks for a really great, clear, informative, thoughtful summary!

I wonder what we could do to get some of the next steps happening sooner, since what typically happens is that we'd wait until we have a pandemic, and then we won't have the necessary data and it will be too late. 

A big challenge I see (as an engineer) is doing the risk/benefit analysis fairly. As EA's, we tend to imagine a rational world where a technology which saves 100 lives but causes two people to suffer serious eye problems would be a success. But in the real world, those 100 people won't even realise their lives have been saved, while those two people will have 50 lawyers calling them up asking them to sue the far-UVC companies and the regulators and officials who approved the system, and sympathetic, uninformed juries ready to award them huge judgments. 

The answer to this, for engineers, has always been getting things into standards (as you mention), so that instead of entering into individual cases, the engineers' defend themselves by proving they followed the standards, and the creators of the standards demonstrate the technical rationale and the experimental data supporting it. 

Standards, predictably, tend to be very conservative. Very few bridges collapse, very few planes crash due to mechanical failure. If you were to do a cost-benefit analysis of the impact of reducing safety standards to the point where we'd have twice as many bridge-collapses and plane-crashes caused by mechanical failure, and put all the money saved into GiveWell-recommended charities, it would surely have a massively positive benefit, but no society would be willing to do this! So the same challenge could be faced here: even a small risk of negative effects will have a huge weighting in any standards. Your idea of far-UVC systems with two settings is intriguing ...

FYI, the review paper that I teased in the introduction has finally been published and is now freely available online. It goes over existing far-UVC skin and eye safety evidence and sketches out important studies that should be done in the future. https://doi.org/10.1111/php.13866

Also, check out these X threads on the paper by Lenni Justen and Kevin Esvelt

This was an extremely helpful post, thank you! 

I really loved this! I have basically no knowledge of the underlying context, but I think this symmary gave me a feel for how detailed and complicated this is (reality has a lot of detail and a lot of societies for air conditioning engineers!), a bit of the actual science, as well as some of the players involved and their incentives.

It's helpful and interesting to look at what small scientific communities are like as analogues for EA research groups.

What are the limitations of the rodent studies? Two ways I could imagine them being inadequate:

  • Rodent eyes are smaller and the physical scale of relevant features matters a lot for how damaging far UV-C is (although I would naively guess that smaller eyes are if anything worse for this, so if the rodents do fine then I'd think the humans would too).
  • Rodents can't follow detailed instructions or provide subjective reports, so some kinds of subtle vision impairments we wouldn't be able to notice.

Do either of these apply, or are the limitations in these studies from other factors?

A somewhat random idea for how far-UVC could be productized (once safety and efficacy are more proven out): Couple it with insurance products.
(Note I thought about this for maybe 20 min in total, so it is a strong take very weakly held)
E.g., sell an insurance against employee sick days (payout per sick day) to employers and install far-UVC in their workplaces as part of the insurance contract. If far-UVC really reduces transmission in offices well enough to warrant the installation costs and provide a benefit on top, this should work out quite well. Most large employers probably have statistics on what sick days cost them each year, so working out a price at which the insurance would be worth taking out could be quite straightforward if one speaks to a few companies (or a consultancy like BCG, Deloitte, McKinsey that sees many organizations).
Some reasons I think this would work: There are similar products in the food sector (e.g., Aanika Biosciences sells insurance against recalls of fresh produce that comes coupled with their DNA tags that allow fast and unequivocal identification of produce origin); insurance against employees taking maternity leave is a thing, so employers know this type of model; selling an insurance like that makes the whole sale a topic for high-level HR rather than building management and I suspect there is more purchasing power in the former than the latter.

Thanks a bunch for this very helpful overview — I'm curating it.

This covers well the things I've learned from my casual observation of the field, and introduced me to new considerations and more detail. I'm very glad to have read it and I recommend it.

Thanks for such a great write-up!

What is needed is a well-powered, carefully controlled real-world trial of far-UVC that uses the number of infections as the primary outcome. Many researchers in the field agree with this need.

  • Only one such trial is currently ongoing, but more needs to be done

The link suggests that the estimated study completion date was April 30, 2023. I couldn't find preliminary results anywhere but I found a talk about it here. It noted that they don't expect Phase 2 –when they actually measure patient outcomes– to end until June 2025 and to only begin their statistical analysis then. (I think to ensure the study is still blinded?)

So still seems like some time to go before we hear about the results! Curious if you think that's different.

(The linked talk was part of the 1st International Congress on Far-UVC Science and Technology, who have uploaded all their videos on their website. A lot of them see very interesting for more details!)

Thanks, Luca!

You are correct that there are no results yet since the trial is still ongoing and double-blinded. I have talked to them about their trial and attended that talk. AFAIK they decided to extend the duration of the trial and are adding another study site (long-term care facility) since they received additional funding for a phase 2. 

In this next phase of the trial, they will also be monitoring ozone and volatile organic compounds, which could provide some useful real-world data about those questions. 

Great summary, I learned a lot. 

Regarding the eye sensitivity, is there any evidence on more vulnerable populations (people with dry eye syndrome or maybe people that have been operated for cataract?) there is no a priori reason they should be that much more sensitive, especially if the eye film isn't responsible for most of the protection anyway, but they are a significant minority of people. 

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