Given that, if I propose an intervention like making homemade masks from fabric which reduced handwashing compliance by 1% (perhaps due to distracting people or making them think handwashing is less critical,) it would need to be astonishingly effective to be net positive. And most such approaches being discussed are, as far as I can tell, nowhere near that level of effectiveness.
This argument depends a lot on the correctness of your model. How do you know which proposals reduce handwashing compliance by 1%? Without numbers, it becomes a fully general argument against doing or even debating anything (other than washing your hands).
Yes, we need to discuss our models. In this case I have some Bayesian priors, informed by a review of relevant literature, and reinforced by observations of how people are actually reacting. I’ve seen many people actually washing their hands recently—not all, but most. And this isn’t usually true, I’ve been paying attention for a couple years now, since I started working in bio-risk. You don’t need to trust my model, but we have fairly strong, if indirect, evidence that many of the proposed interventions—like mask wearing by people who aren’t trained to do so, which I keeps seeing, and it would be funny if it weren’t infuriating—are marginal at best.
That paper (which I notice you’re first author on) is pretty good and you might want to post it as a top-level post. Note that you estimate handwashing optimistically reduces transmission by 50%. This paper estimated an R0 in Wuhan of 3.86 prior to social distancing measures, so if the situation in other cities is similar, then high compliance with hand-washing would only cover about half of the required reduction, with the rest left to other measures such as reduction in gatherings and travel.
I posted in to the EA forum, and have now crossposted that to Lesswrong. (I clearly overestimated the proportion of people who read both.)
Regarding transmission reduction from handwashing, two points. First, reducing R0 flattens the curve in ways that make the epidemic far more manageable for emergency services, saving lives. Second, prior to any social distancing, the R_0 was far higher than it is when we have the growing norms around reduced hand-contact, etc., which could very plausibly combine to push R0 far closer to 1.
Just curious, does anyone have a link to a paper estimating the effectiveness of masks when not worn properly? My intuition says that I would expect them to be somewhat less effective (maybe 50%), but that a lot of the effect would still be present.
I’ve spend 15 minutes looking for a good paper, but haven’t found one. This is a claim I’ve seen cited many times, so it seems good to ground it out.
After researching this for another 40 minutes, I still don’t see where this claim comes from. All studies that I found are talking about adherence in the form of “was wearing the mask most of the time”, and I can’t find any analysis that wearing a mask is super complicated, and that people are wearing the masks in an ineffective way (many sources say that it’s hard to get people to wear the masks at all, but that’s a different issue).
When you gave a group of people a set of masks, the people who comply to the level of “are wearing the mask most of the time” appear to be experiencing a significant reduction in infection rates. This is true even if the masks weren’t fitted. Here is one of the variety of studies I found about this.
I currently don’t believe the “masks worn by people who aren’t trained to do so aren’t effective” claim. I also further believe that the effect of masks on untrained people is on the same order of magnitude as hand-washing (though definitely smaller, my gut says something like a 4th to a 5th as effective), and as such is not marginal. Though the latter claim is definitely not super well-sourced and I haven’t done the appropriate fermi estimates, and would greatly appreciate more evidence on the relative importance of these interventions.
I think it’s also worth pointing out that there just aren’t enough masks for what you are suggesting. That’s why my example was telling people to make homemade masks, not using N95 respirators. If they are following instructions for mask usage, people should be replacing masks multiple times every day and not reusing them—as soon as you remove the mask, you touch both the inside and the outside, moving droplets around. Suggesting widespread use of the types of masks you’re talking about, then, seems unhelpful in any case.
That’s a very useful data point, and I’m happy to see that I was pessimistic about how quickly factories could ramp up production. Hopefully we’ll see the supply crunch reduced in the near future, (without a collapse in quality,) and at that point I’d be very happy for people to advocate more widespread mask wearing using actual disposable masks.
There is research on loosely fit mask like surgical mask effectiveness compared to fit respirators, and they are much less effective. My model here is that loose fitting masks that prevent 50% - or even 95% of the particles from reaching your mouth is near-useless if someone sneezes on you, since you don’t need more than a very small number of particles to infect you. And otherwise, masks for non-sick people aren’t accomplishing much without handwashing after every time they touch the mask—especially when people still touch their mouths behind their masks, as people often do even when they know they are aerosolizing dangerous pathogens in labs. To reinforce this, anecdotally, biosafety lab workers go through training, and still need routine retraining to make sure they wear masks properly and don’t do things like eat with masks on by moving the mask out of the way.
Do you have any source for this? I remember multiple claiming that this research exists, but as I mentioned, I have so far failed to find it. The “near-useless” claim also appears to be contradicted by the study I linked in the other comment:
We estimated that, irrespective of the assumed value for the incubation period (1 or 2 days), the relative reduction in the daily risk of acquiring a respiratory infection associated with adherent mask use (P2 or surgical) was in the range of 60%–80%
Which seems like a really large amount, and was for non-fitted masks.
Thanks for that, and I have updated towards masks being more useful for non-infected people to prevent getting sick than I previously thought—though not much for the usefulness of advocating mask wearing for the public, given shortages.
I do suspect that the poorly fitting masks were useful for other reasons, like reducing hand-to-mouth contacts and increasing handwashing—which was reported as 10% higher for adherent mask wearers than non-adherent ones, potentially contributing to the effect. (It was unfortunately not reported for the control group.)
This argument depends a lot on the correctness of your model. How do you know which proposals reduce handwashing compliance by 1%? Without numbers, it becomes a fully general argument against doing or even debating anything (other than washing your hands).
Yes, we need to discuss our models. In this case I have some Bayesian priors, informed by a review of relevant literature, and reinforced by observations of how people are actually reacting. I’ve seen many people actually washing their hands recently—not all, but most. And this isn’t usually true, I’ve been paying attention for a couple years now, since I started working in bio-risk. You don’t need to trust my model, but we have fairly strong, if indirect, evidence that many of the proposed interventions—like mask wearing by people who aren’t trained to do so, which I keeps seeing, and it would be funny if it weren’t infuriating—are marginal at best.
That paper (which I notice you’re first author on) is pretty good and you might want to post it as a top-level post. Note that you estimate handwashing optimistically reduces transmission by 50%. This paper estimated an R0 in Wuhan of 3.86 prior to social distancing measures, so if the situation in other cities is similar, then high compliance with hand-washing would only cover about half of the required reduction, with the rest left to other measures such as reduction in gatherings and travel.
I posted in to the EA forum, and have now crossposted that to Lesswrong. (I clearly overestimated the proportion of people who read both.)
Regarding transmission reduction from handwashing, two points. First, reducing R0 flattens the curve in ways that make the epidemic far more manageable for emergency services, saving lives. Second, prior to any social distancing, the R_0 was far higher than it is when we have the growing norms around reduced hand-contact, etc., which could very plausibly combine to push R0 far closer to 1.
Just curious, does anyone have a link to a paper estimating the effectiveness of masks when not worn properly? My intuition says that I would expect them to be somewhat less effective (maybe 50%), but that a lot of the effect would still be present.
I’ve spend 15 minutes looking for a good paper, but haven’t found one. This is a claim I’ve seen cited many times, so it seems good to ground it out.
After researching this for another 40 minutes, I still don’t see where this claim comes from. All studies that I found are talking about adherence in the form of “was wearing the mask most of the time”, and I can’t find any analysis that wearing a mask is super complicated, and that people are wearing the masks in an ineffective way (many sources say that it’s hard to get people to wear the masks at all, but that’s a different issue).
When you gave a group of people a set of masks, the people who comply to the level of “are wearing the mask most of the time” appear to be experiencing a significant reduction in infection rates. This is true even if the masks weren’t fitted. Here is one of the variety of studies I found about this.
I currently don’t believe the “masks worn by people who aren’t trained to do so aren’t effective” claim. I also further believe that the effect of masks on untrained people is on the same order of magnitude as hand-washing (though definitely smaller, my gut says something like a 4th to a 5th as effective), and as such is not marginal. Though the latter claim is definitely not super well-sourced and I haven’t done the appropriate fermi estimates, and would greatly appreciate more evidence on the relative importance of these interventions.
I think it’s also worth pointing out that there just aren’t enough masks for what you are suggesting. That’s why my example was telling people to make homemade masks, not using N95 respirators. If they are following instructions for mask usage, people should be replacing masks multiple times every day and not reusing them—as soon as you remove the mask, you touch both the inside and the outside, moving droplets around. Suggesting widespread use of the types of masks you’re talking about, then, seems unhelpful in any case.
Oh, I am not at all advocating for widespread usage of masks in this particular pandemic. I am just trying to figure out whether they are effective.
However, on a more object-level, see this comment for an estimate of the potential increase of global mask production in the next few months.
That’s a very useful data point, and I’m happy to see that I was pessimistic about how quickly factories could ramp up production. Hopefully we’ll see the supply crunch reduced in the near future, (without a collapse in quality,) and at that point I’d be very happy for people to advocate more widespread mask wearing using actual disposable masks.
There is research on loosely fit mask like surgical mask effectiveness compared to fit respirators, and they are much less effective. My model here is that loose fitting masks that prevent 50% - or even 95% of the particles from reaching your mouth is near-useless if someone sneezes on you, since you don’t need more than a very small number of particles to infect you. And otherwise, masks for non-sick people aren’t accomplishing much without handwashing after every time they touch the mask—especially when people still touch their mouths behind their masks, as people often do even when they know they are aerosolizing dangerous pathogens in labs. To reinforce this, anecdotally, biosafety lab workers go through training, and still need routine retraining to make sure they wear masks properly and don’t do things like eat with masks on by moving the mask out of the way.
Do you have any source for this? I remember multiple claiming that this research exists, but as I mentioned, I have so far failed to find it. The “near-useless” claim also appears to be contradicted by the study I linked in the other comment:
https://www.ncbi.nlm.nih.gov/pubmed/19193267
Which said:
Which seems like a really large amount, and was for non-fitted masks.
Thanks for that, and I have updated towards masks being more useful for non-infected people to prevent getting sick than I previously thought—though not much for the usefulness of advocating mask wearing for the public, given shortages.
I do suspect that the poorly fitting masks were useful for other reasons, like reducing hand-to-mouth contacts and increasing handwashing—which was reported as 10% higher for adherent mask wearers than non-adherent ones, potentially contributing to the effect. (It was unfortunately not reported for the control group.)