Perhaps I am missing something but on the >=1000x criteria, if we target e.g. <1% of people succumbing to the disease over their lifetime (might want to set even lower, in order to make people comply with suggestions—precedent of similar risk reductions and uptake might be worth looking into if not done already), this means we expect people that are not protected to inhale only 10 particles over their lifetime, in expectation (assuming minimum lethal dose of 1 particle)? Asking as that seems like a small degree of environmental spread. I realize that perhaps the reasoning here might be infohazardous, but if not I would be very interested to know more. Or perhaps additional reduction comes from one or more additional measures, such as far UVC, glycol, etc.
Agreed that the 3-log reduction is appropriate for cases where the “baseline” dose is pretty low. Our team is still uncertain about what protection level might be needed, but has some high-level reasons to expect that background environment-to-human (E2H) aerosol pathogen concentrations are likely low in many environments.
One reason is that airborne microbial concentrations and species composition vary a lot across environments. Existing microbial ecosystems also tend to be quite diverse, so even the most common bacterial species often make up only a small share of total bacteria. Likewise, an E2H pathogen, such as a mirror bacterium, probably wouldn’t become highly concentrated across most natural ecosystems. While mirror bacteria might not face the same predation pressures as many other bacteria, they would still have to compete for resources and wouldn’t necessarily occupy a large share of many ecological niches. So even though outdoor air can contain thousands to millions of bacteria per cubic meter, mirror bacteria probably wouldn’t be present at high concentrations in many outdoor environments. To the extent concentrations vary substantially by location, there might also be places with much lower exposure risk.
There are also reasons to expect that the infectious dose wouldn’t necessarily be one bacterium. Even if human immune systems did not respond to mirror bacteria, our respiratory tracts have physical defenses, such as blocking or clearing inhaled particles, and bacteria do not automatically colonize every environment they land in. The BPP team is very unsure what an infectious dose might be, and it could be low—for infections like Q fever and TB, I think the infectious dose is quite low—but it is not guaranteed to be low for E2H pathogens.
Last, the 3-log reduction is what our team currently thinks could buy humanity enough run room to find better solutions, such as building better protections or developing and mass-producing medical countermeasures (MCMs). So the 3-log protection doesn’t need to provide perfect protection for someone’s whole life, but might just keep people alive for a year or a few years. Also, in the early stages of an E2H pathogen release, while humanity is increasing resilience through better protection options or MCMs, concentrations might still be lower as the pathogen spreads, so the threshold for useful protection might be lower.
Sure — I may be mixing abstractions here, so let me spell out what I had in mind.
A 1000× reduction means that, in expectation, the protected environment has 1/1000 of the relevant airborne particle concentration compared with the outside environment. So if an unprotected person would inhale 1000 relevant particles over some period, a protected person would inhale about 1 over the same period, ignoring spatial variation, time dynamics, leakage events, deposition, behavior, etc.
My intuition was then: if the minimum infectious/lethal dose were effectively 1 particle, and if we wanted lifetime infection/death risk inside the protected space to be below ~1%, then the protected person’s expected inhaled dose would need to be on the order of <0.01 infectious particles over the relevant period. With only a 1000× reduction, that corresponds to an outside unprotected expected inhaled dose of only ~10 infectious particles over that same period.
That seems surprisingly low compared to my own work on mirror bacteria. So I was wondering whether the 1000× target assumes one or more of the following:
the relevant environmental concentrations are expected to be quite low;
the true infectious/lethal dose is meaningfully above 1 particle;
the 1000× PM10 reduction is only one layer, with additional reductions from UV, glycol vapor, surface controls, masks, behavior, etc.;
the target is meant as a practical near-term benchmark rather than a complete risk-reduction target.
So my question is basically: what outside concentration / dose / acceptable-risk model makes 1000× the right threshold?
Perhaps I am missing something but on the >=1000x criteria, if we target e.g. <1% of people succumbing to the disease over their lifetime (might want to set even lower, in order to make people comply with suggestions—precedent of similar risk reductions and uptake might be worth looking into if not done already), this means we expect people that are not protected to inhale only 10 particles over their lifetime, in expectation (assuming minimum lethal dose of 1 particle)? Asking as that seems like a small degree of environmental spread. I realize that perhaps the reasoning here might be infohazardous, but if not I would be very interested to know more. Or perhaps additional reduction comes from one or more additional measures, such as far UVC, glycol, etc.
Agreed that the 3-log reduction is appropriate for cases where the “baseline” dose is pretty low. Our team is still uncertain about what protection level might be needed, but has some high-level reasons to expect that background environment-to-human (E2H) aerosol pathogen concentrations are likely low in many environments.
One reason is that airborne microbial concentrations and species composition vary a lot across environments. Existing microbial ecosystems also tend to be quite diverse, so even the most common bacterial species often make up only a small share of total bacteria. Likewise, an E2H pathogen, such as a mirror bacterium, probably wouldn’t become highly concentrated across most natural ecosystems. While mirror bacteria might not face the same predation pressures as many other bacteria, they would still have to compete for resources and wouldn’t necessarily occupy a large share of many ecological niches. So even though outdoor air can contain thousands to millions of bacteria per cubic meter, mirror bacteria probably wouldn’t be present at high concentrations in many outdoor environments. To the extent concentrations vary substantially by location, there might also be places with much lower exposure risk.
There are also reasons to expect that the infectious dose wouldn’t necessarily be one bacterium. Even if human immune systems did not respond to mirror bacteria, our respiratory tracts have physical defenses, such as blocking or clearing inhaled particles, and bacteria do not automatically colonize every environment they land in. The BPP team is very unsure what an infectious dose might be, and it could be low—for infections like Q fever and TB, I think the infectious dose is quite low—but it is not guaranteed to be low for E2H pathogens.
Last, the 3-log reduction is what our team currently thinks could buy humanity enough run room to find better solutions, such as building better protections or developing and mass-producing medical countermeasures (MCMs). So the 3-log protection doesn’t need to provide perfect protection for someone’s whole life, but might just keep people alive for a year or a few years. Also, in the early stages of an E2H pathogen release, while humanity is increasing resilience through better protection options or MCMs, concentrations might still be lower as the pathogen spreads, so the threshold for useful protection might be lower.
I don’t quite follow, can you spell out the reasoning a bit more?
Sure — I may be mixing abstractions here, so let me spell out what I had in mind.
A 1000× reduction means that, in expectation, the protected environment has 1/1000 of the relevant airborne particle concentration compared with the outside environment. So if an unprotected person would inhale 1000 relevant particles over some period, a protected person would inhale about 1 over the same period, ignoring spatial variation, time dynamics, leakage events, deposition, behavior, etc.
My intuition was then: if the minimum infectious/lethal dose were effectively 1 particle, and if we wanted lifetime infection/death risk inside the protected space to be below ~1%, then the protected person’s expected inhaled dose would need to be on the order of <0.01 infectious particles over the relevant period. With only a 1000× reduction, that corresponds to an outside unprotected expected inhaled dose of only ~10 infectious particles over that same period.
That seems surprisingly low compared to my own work on mirror bacteria. So I was wondering whether the 1000× target assumes one or more of the following:
the relevant environmental concentrations are expected to be quite low;
the true infectious/lethal dose is meaningfully above 1 particle;
the 1000× PM10 reduction is only one layer, with additional reductions from UV, glycol vapor, surface controls, masks, behavior, etc.;
the target is meant as a practical near-term benchmark rather than a complete risk-reduction target.
So my question is basically: what outside concentration / dose / acceptable-risk model makes 1000× the right threshold?
Thanks, I follow you now.