8 ms·

As I understand it, this study concludes that their index of mask use (based on the University of Washington's IHME data) correlates with infection minima, but

As I understand it, this study concludes that their index of mask use (based on the University of Washington's IHME data) correlates with infection minima, but not the maxima. In other words, a higher rate of mask use helps keep COVID-19 levels low when they are low, but doesn't seem to slow them down when infection rates rise. There's overwhelming evidence that mask use is effective in retarding the spread of COVID-19 (e.g., https://jamanetwork.com/journals/jama/fullarticle/2776536 https://jamanetwork.com/journals/jama/fullarticle/2776536, https://science.sciencemag.org/content/372/6549/1439 https://science.sciencemag.org/content/372/6549/1439, and many others). So I suspect that what's happening here is that mask use keeps the rates low among the masked, but once the infection rate takes off among the unmasked, there are enough vulnerable individuals to render the pool effectively infinite from the virus's point of view, and the number of masked individuals becomes irrelevant since they have no effect on the large, vulnerable unmasked pool.

vannevar 5y ago
Would the downvoters care to share their perspective, and/or evidence to the contrary?
- mikem170 5y ago
  Not a downvoter, but I'm sceptical of your conclusion. I took a look at the contents of the report, and it is denser than most. I was looking for some idea of the magnitude of difference that you are seeing, and wasn't sure that I was looking in the right place. Beyond that I wonder what your premise amounts to. Waves of covid come and go in masked and unmasked states. What does it mean to say that masks slow growth at infection minima when a wave comes along and cases grow to a maxima despite the masks? I'm still chewing on this, but thought I'd throw this out there since you asked.
  - vannevar 5y ago
    There are a lot of details in the paper, but the relevant conclusion is in the 'Results' section of the abstract: "Mask use predicted lower minimum but not lower maximum growth rates." The explanation that I offered is that, at low infection rates, people's probability of exposure is roughly the same whether or not they wear a mask, though their chance of infection is very different. This drags down the rate of infection proportionately to the number of masked people. Once the virus makes inroads in the unmasked community, however, the chance of an unmasked person getting exposed becomes steadily greater and greater, because an unmasked person is more likely to be around other unmasked people, which means that not only do they have a higher (relatively fixed) risk of being infected when exposed, they also have an increasingly high risk of being exposed. Then the exponentially increasing infections among the unmasked swamp the lower, relatively fixed rate at which the masked get infected.
    - mikem170 5y ago
      But then why do masked populations end up with the same maximum growth rate? Doesn't that mean that mask populations end up catching it the same in the end? Wondering this, I wasn't sure of the significance of what you are saying. Also I wondered what is the magnitude of the different predicted lower minimum that the paper talks about is? i.e. 5% or 25% or 125%, etc. Some of those mask studies you linked to earlier were not great studies. I didn't click through everything, but for example the hairdresser study that one of them link to had no control (no hairdresser without a mask for comparison), confounding factors (hand hygiene compared to population, ventilation), and they didn't test all the customers (self reporting, also they didn't test customers from before the stylists developed symptoms (when they may have been at their most contagious). The USS Theodore Roosevelt study also mentioned had a lot going on, I wondered how they separated the self-reported mix of precautions (masks, social distancing, and common area avoidance), given the relatively small sample size for so many variables. I didn't look through the rest. On the other hand... Here's a randomized control trial covid mask study [0] involving 4800+ people that shows surgical mask wearing was not statistically significantly better than no mask. Here's another study [1] (pre-covid) involving 1600 people working in hospitals that shows cloth masks are penetrated by 97% of particles, compared to 44% for surgical masks. The authors of this study say that cloth masks may potentially increase infection risk, double masking making it worse (holding viruses particles near the face and moist breath). Another pre-covid paper [2] that analyzed 9 studies on medical/surgical masks (3500+ participants total) and concluded "wearing a mask may make little to no difference in how many people caught a flu‐like illness". I find the gap between what politicians and the media have been saying and these studies to be disturbing. But maybe this is why the CDC retracted their mask recommendation for vaccinated individuals several months ago, because the data doesn't show that masks help. [0] https://pubmed.ncbi.nlm.nih.gov/33205991/ https://pubmed.ncbi.nlm.nih.gov/33205991/ [1] https://www.researchgate.net/publication/275360639_A_cluster_randomised_trial_of_cloth_masks_compared_with_medical_masks_in_healthcare_workers https://www.researchgate.net/publication/275360639_A_cluster... [2] https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006207.pub5/full https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD...
      - vannevar 5y ago
criticaltinker 5y ago
> There's overwhelming evidence that mask use is effective in retarding the spread of COVID-19 It's probably not fair to phrase it as overwhelming evidence. Yes there is evidence that masks can reduce transmission, and the citations you provided included a fair amount of research supporting this idea (thanks for those references). And just thinking about it logically, it seems obvious masks would have such an effect. However the evidence presented in OP - and the previous studies it cited - provide counter-evidence suggesting that mask usage and mandates may not have a significant beneficial impact on the overall course of a pandemic. There are a variety of possible reasons for this, which you began to speculate on. Poor compliance, people not wearing their masks correctly, porous cloth masks, poorly ventilated indoor environments contributing to high viral load environments even with 100% mask compliance - the number of places where things can go wrong are tremendous and it begs the question of if the tradeoffs of mask mandates are worth it, or if our resources would be better spent on other viral elimination strategies.
- vannevar 5y ago
  I should probably rephrase that as overwhelming evidence that they are effective in a clinical setting---ie, in a lab, and in medical settings. The point is, if you're sitting in a room with an infected person, there have been many studies that show that you will get a lower exposure if you're masked, and a much lower exposure if the infected person is masked as well. I posted a more detailed explanation of my theory above. You don't need to account for imperfections in masks, or ventilation, or any other details. Even if you make the assumption that masks are perfectly effective, the observations seen by the researchers might be explained by exponentially increasing spread among the unmasked. To use an analogy, a 4' child can drown just as easily in a 5' deep pool as in 100' deep lake. The percentage of mask usage referenced in the paper would only dictate the depth of the pool, so it's not surprising it would have little effect once the virus takes hold in the unmasked population. Barring very high mask usage (making the pool only 2' deep, to continue the analogy), exponential infection spikes in the unmasked population are unavoidable. It doesn't mean masks don't work, it only indicates just how high usage needs to be to stop these spikes.

vannevar 5y ago

Would the downvoters care to share their perspective, and/or evidence to the contrary?

mikem170 5y ago
Not a downvoter, but I'm sceptical of your conclusion. I took a look at the contents of the report, and it is denser than most. I was looking for some idea of the magnitude of difference that you are seeing, and wasn't sure that I was looking in the right place. Beyond that I wonder what your premise amounts to. Waves of covid come and go in masked and unmasked states. What does it mean to say that masks slow growth at infection minima when a wave comes along and cases grow to a maxima despite the masks? I'm still chewing on this, but thought I'd throw this out there since you asked.
- vannevar 5y ago
  There are a lot of details in the paper, but the relevant conclusion is in the 'Results' section of the abstract: "Mask use predicted lower minimum but not lower maximum growth rates." The explanation that I offered is that, at low infection rates, people's probability of exposure is roughly the same whether or not they wear a mask, though their chance of infection is very different. This drags down the rate of infection proportionately to the number of masked people. Once the virus makes inroads in the unmasked community, however, the chance of an unmasked person getting exposed becomes steadily greater and greater, because an unmasked person is more likely to be around other unmasked people, which means that not only do they have a higher (relatively fixed) risk of being infected when exposed, they also have an increasingly high risk of being exposed. Then the exponentially increasing infections among the unmasked swamp the lower, relatively fixed rate at which the masked get infected.
  - mikem170 5y ago
    But then why do masked populations end up with the same maximum growth rate? Doesn't that mean that mask populations end up catching it the same in the end? Wondering this, I wasn't sure of the significance of what you are saying. Also I wondered what is the magnitude of the different predicted lower minimum that the paper talks about is? i.e. 5% or 25% or 125%, etc. Some of those mask studies you linked to earlier were not great studies. I didn't click through everything, but for example the hairdresser study that one of them link to had no control (no hairdresser without a mask for comparison), confounding factors (hand hygiene compared to population, ventilation), and they didn't test all the customers (self reporting, also they didn't test customers from before the stylists developed symptoms (when they may have been at their most contagious). The USS Theodore Roosevelt study also mentioned had a lot going on, I wondered how they separated the self-reported mix of precautions (masks, social distancing, and common area avoidance), given the relatively small sample size for so many variables. I didn't look through the rest. On the other hand... Here's a randomized control trial covid mask study [0] involving 4800+ people that shows surgical mask wearing was not statistically significantly better than no mask. Here's another study [1] (pre-covid) involving 1600 people working in hospitals that shows cloth masks are penetrated by 97% of particles, compared to 44% for surgical masks. The authors of this study say that cloth masks may potentially increase infection risk, double masking making it worse (holding viruses particles near the face and moist breath). Another pre-covid paper [2] that analyzed 9 studies on medical/surgical masks (3500+ participants total) and concluded "wearing a mask may make little to no difference in how many people caught a flu‐like illness". I find the gap between what politicians and the media have been saying and these studies to be disturbing. But maybe this is why the CDC retracted their mask recommendation for vaccinated individuals several months ago, because the data doesn't show that masks help. [0] https://pubmed.ncbi.nlm.nih.gov/33205991/ https://pubmed.ncbi.nlm.nih.gov/33205991/ [1] https://www.researchgate.net/publication/275360639_A_cluster_randomised_trial_of_cloth_masks_compared_with_medical_masks_in_healthcare_workers https://www.researchgate.net/publication/275360639_A_cluster... [2] https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD006207.pub5/full https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD...
    - vannevar 5y ago

criticaltinker 5y ago

> There's overwhelming evidence that mask use is effective in retarding the spread of COVID-19 It's probably not fair to phrase it as overwhelming evidence. Yes there is evidence that masks can reduce transmission, and the citations you provided included a fair amount of research supporting this idea (thanks for those references). And just thinking about it logically, it seems obvious masks would have such an effect. However the evidence presented in OP - and the previous studies it cited - provide counter-evidence suggesting that mask usage and mandates may not have a significant beneficial impact on the overall course of a pandemic. There are a variety of possible reasons for this, which you began to speculate on. Poor compliance, people not wearing their masks correctly, porous cloth masks, poorly ventilated indoor environments contributing to high viral load environments even with 100% mask compliance - the number of places where things can go wrong are tremendous and it begs the question of if the tradeoffs of mask mandates are worth it, or if our resources would be better spent on other viral elimination strategies.

vannevar 5y ago
I should probably rephrase that as overwhelming evidence that they are effective in a clinical setting---ie, in a lab, and in medical settings. The point is, if you're sitting in a room with an infected person, there have been many studies that show that you will get a lower exposure if you're masked, and a much lower exposure if the infected person is masked as well. I posted a more detailed explanation of my theory above. You don't need to account for imperfections in masks, or ventilation, or any other details. Even if you make the assumption that masks are perfectly effective, the observations seen by the researchers might be explained by exponentially increasing spread among the unmasked. To use an analogy, a 4' child can drown just as easily in a 5' deep pool as in 100' deep lake. The percentage of mask usage referenced in the paper would only dictate the depth of the pool, so it's not surprising it would have little effect once the virus takes hold in the unmasked population. Barring very high mask usage (making the pool only 2' deep, to continue the analogy), exponential infection spikes in the unmasked population are unavoidable. It doesn't mean masks don't work, it only indicates just how high usage needs to be to stop these spikes.