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.
    • You can watch recordings of the talks!
  • 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):
  • Open Philanthropy
    • Seem to be becoming increasingly interested in far-UVC. They recently put out a Request for Information: Evaluation of Germicidal Far-UVC: Safety, Efficacy, Technology, and Adoption 
    • Open Phil has funded far-UVC research in the past, e.g. at Columbia (Brenner group).
  • Convergent Research
    • Have mostly worked on understanding the current landscape of far-UVC sources/emitters and how emitter tech development is moving forward
    • Convergent Research is dedicated to setting up Focused Research Organizations (FROs), so they are trying to scope out whether it could make sense to set up a FRO around far-UVC
  • 1DaySooner
    • Published a report on indoor air quality, including a discussion of GUV: Air Safety to Combat Global Catastrophic Biorisk
  • Rethink Priorities
    • Ran surveys to asses the US public’s perception of germicidal UV
• 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.