My current understanding is that masks work by keeping you from spreading virus. If you don’t have the virus, wearing a mask is useless.
That’s an overstatement, by my understanding. Masks are better at stopping outgoing germs than incoming ones, but they still do some good for both directions.
“All recruits wore double-layered cloth masks at all times indoors and outdoors, except when sleeping or eating; practiced social distancing of at least 6 feet; were not allowed to leave campus; did not have access to personal electronics and other items that might contribute to surface transmission; and routinely washed their hands. They slept in double-occupancy rooms with sinks, ate in shared dining facilities, and used shared bathrooms. All recruits cleaned their rooms daily, sanitized bathrooms after each use with bleach wipes, and ate preplated meals in a dining hall that was cleaned with bleach after each platoon had eaten. Most instruction and exercises were conducted outdoors. All movement of recruits was supervised, and unidirectional flow was implemented, with designated building entry and exit points to minimize contact among persons.”
Looks like they did quite a bit more than “wear masks”. Plus, note double-layered masks...
Looks like they did quite a bit more than “wear masks”. Plus, note double-layered masks...
Yes, given the amount that they did you would expect a clear effect if masks do a decent job at protecting wearers.
One possible explanation is that COVID-19 mostly spreads through aerosol transmissions where a cloth masks doesn’t do a good job.
If that scenario is true measures for air quality are more important for mask wearing. I still believe that there are conditions where it makes sense to wear a mask because of the precautionary principle, but as the title of this post suggests the evidence really isn’t that clear.
The most important bit here is not “double-layered”; it’s “all recruits”. There was no unmasked group for comparison, so this study tells us nothing about mask effectiveness beyond “some people still got infected, so they’re less than 100% effective”.
This sounds like you basically don’t believe in Evidence-Based Medicine and form your believe based on simple pathopathological models (the thing that Evidence-Based Medicine was about to fight) or don’t care about mask wearing to form an informed opinion about it.
To recap, there are actual studies on mask wearing. One of them is SARS-CoV-2 Transmission among Marine Recruits during Quarantine. The benefit of studying military recruits is that it’s likely the best group for complience to policies as the training instructors made sure that they were wearing their masks.
I now this might sound harsh but “I think you are wrong because of “one sentence pathopathological models’” is not the kind of argument I like to see on LessWrong from people who haven’t done any research to be familiar with the topic.
It’s not that I believe that you should always reason in an Evidence-Based manner, but be at least a bit more sophisticated about it.
It’s not that I “don’t believe in Evidence-Based Medicine”, it’s that you didn’t mention in your first comment that your were talking about a different study, so I really didn’t know what you were talking about. Thanks for giving the link.
The Marine study doesn’t address the effects of masks. Both the participants and nonparticipants wore masks. The actual difference between those groups was that the participants were asked about symptoms, tested, and isolated if positive at day 0, 7, and 14, versus only on day 14 for nonparticipants. It gives us some (unsurprising) evidence that surveillance testing and isolation helps: on day 14, at least 11/1760 (0.6%) and possibly as many as 22/1847 (1.2%) participants were positive, compared to 26/1554 (1.7%) nonparticipants. Unfortunately the reporting is not great, so we don’t know exactly how many participants were positive on day 14. And this is pretty weak evidence: we don’t know how many of the nonparticipants would have tested positive at day 0, so it’s hard to say how much of the day-14 difference was due to weeding out infected participants versus the participants possibly starting with a lower infection rate.
That’s an overstatement, by my understanding. Masks are better at stopping outgoing germs than incoming ones, but they still do some good for both directions.
Why do you believe there wasn’t a significant effect of mask wearing in the military recruits if not because the masks didn’t protect the wearer?
“All recruits wore double-layered cloth masks at all times indoors and outdoors, except when sleeping or eating; practiced social distancing of at least 6 feet; were not allowed to leave campus; did not have access to personal electronics and other items that might contribute to surface transmission; and routinely washed their hands. They slept in double-occupancy rooms with sinks, ate in shared dining facilities, and used shared bathrooms. All recruits cleaned their rooms daily, sanitized bathrooms after each use with bleach wipes, and ate preplated meals in a dining hall that was cleaned with bleach after each platoon had eaten. Most instruction and exercises were conducted outdoors. All movement of recruits was supervised, and unidirectional flow was implemented, with designated building entry and exit points to minimize contact among persons.”
Looks like they did quite a bit more than “wear masks”. Plus, note double-layered masks...
Yes, given the amount that they did you would expect a clear effect if masks do a decent job at protecting wearers.
One possible explanation is that COVID-19 mostly spreads through aerosol transmissions where a cloth masks doesn’t do a good job.
If that scenario is true measures for air quality are more important for mask wearing. I still believe that there are conditions where it makes sense to wear a mask because of the precautionary principle, but as the title of this post suggests the evidence really isn’t that clear.
The most important bit here is not “double-layered”; it’s “all recruits”. There was no unmasked group for comparison, so this study tells us nothing about mask effectiveness beyond “some people still got infected, so they’re less than 100% effective”.
What military recruits are you talking about? I didn’t see any reference to the military.
This sounds like you basically don’t believe in Evidence-Based Medicine and form your believe based on simple pathopathological models (the thing that Evidence-Based Medicine was about to fight) or don’t care about mask wearing to form an informed opinion about it.
To recap, there are actual studies on mask wearing. One of them is SARS-CoV-2 Transmission among Marine Recruits during Quarantine. The benefit of studying military recruits is that it’s likely the best group for complience to policies as the training instructors made sure that they were wearing their masks.
I now this might sound harsh but “I think you are wrong because of “one sentence pathopathological models’” is not the kind of argument I like to see on LessWrong from people who haven’t done any research to be familiar with the topic.
It’s not that I believe that you should always reason in an Evidence-Based manner, but be at least a bit more sophisticated about it.
It’s not that I “don’t believe in Evidence-Based Medicine”, it’s that you didn’t mention in your first comment that your were talking about a different study, so I really didn’t know what you were talking about. Thanks for giving the link.
The Marine study doesn’t address the effects of masks. Both the participants and nonparticipants wore masks. The actual difference between those groups was that the participants were asked about symptoms, tested, and isolated if positive at day 0, 7, and 14, versus only on day 14 for nonparticipants. It gives us some (unsurprising) evidence that surveillance testing and isolation helps: on day 14, at least 11/1760 (0.6%) and possibly as many as 22/1847 (1.2%) participants were positive, compared to 26/1554 (1.7%) nonparticipants. Unfortunately the reporting is not great, so we don’t know exactly how many participants were positive on day 14. And this is pretty weak evidence: we don’t know how many of the nonparticipants would have tested positive at day 0, so it’s hard to say how much of the day-14 difference was due to weeding out infected participants versus the participants possibly starting with a lower infection rate.
Correction: for participants on day 14, it was somewhere between 11 and 33 out of 1847 (0.6%-1.8%). Not that it makes much of a difference.