Effectiveness of public health measures

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shpalman
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Effectiveness of public health measures

Post by shpalman » Thu Nov 18, 2021 11:09 am

Effectiveness of public health measures in reducing the incidence of covid-19, SARS-CoV-2 transmission, and covid-19 mortality: systematic review and meta-analysis

BMJ 2021;375:e068302 https://doi.org/10.1136/bmj-2021-068302

Written about in The Guardian who still haven't realized that you can link from one thing on the web to another thing on the web.

It's about investigating "the effect of mask wearing, handwashing, and physical distancing measures on incidence of covid-19".

Image

The tl;dr seems to be that wearing masks has a useful effect.
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Re: Effectiveness of public health measures

Post by Herainestold » Thu Nov 18, 2021 5:01 pm

53% seems high.

Mask wearing combined with lockdowns and border controls would do a lot to get us out of our current predicament.
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Re: Effectiveness of public health measures

Post by Herainestold » Fri Nov 19, 2021 1:41 am

John Burne Murdoch says:
Let’s start by saying that yes, we have good evidence that masks reduce Covid incidence.

BUT it points to nowhere near a 53% reduction. As today’s @bmj_latest
states, the best evidence — randomised controlled trials — point to more like a 10% cut
https://twitter.com/jburnmurdoch/status ... 7653317640
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Re: Effectiveness of public health measures

Post by shpalman » Fri Nov 19, 2021 9:22 am

Well I also found it interesting that they did a meta-analysis of one study, but then it's also interesting that reviewer 2 seems to want to reject it but they publish it anyway with reviewer 2's comments as an editorial.

But that study involving more than 340,000 people in Bangladesh wasn't about mask wearing vs. non mask wearing, it was about telling people to wear masks and giving them free ones vs. not doing that.

https://www.poverty-action.org/sites/de ... 083121.pdf
All intervention arms received free masks, information on the importance of masking, role modeling by community leaders, and in-person reminders for 8 weeks. The control group did not receive any interventions.
The intervention increased proper mask-wearing from 13.3% in control villages (N=806,547 observations) to 42.3% in treatment villages (N=797,715 observations) (adjusted percentage point difference = 0.29 [0.27, 0.31]). This tripling of mask usage was sustained during the intervention period and two weeks after.
...
The proportion of individuals with COVID-like symptoms was 7.62% (N=13,273) in the intervention arm and 8.62% (N=13,893) in the control arm. Blood samples were collected from N=10,952 consenting, symptomatic individuals. Adjusting for baseline covariates, the intervention reduced symptomatic seroprevalence by 9.3% (adjusted prevalence ratio (aPR) = 0.91 [0.82, 1.00]; control prevalence 0.76%; treatment prevalence 0.68%). In villages randomized to surgical masks (n = 200), the relative reduction was 11.2% overall (aPR = 0.89 [0.78, 1.00]) and 34.7% among individuals 60+ (aPR = 0.65 [0.46, 0.85]). No adverse events were reported.
So that 9.3% reduction in symptomatic seroprevalence isn't coming from 100% mask wearing vs. 0% mask wearing, but rather 42.3% mask wearing vs. 13.3% mask wearing.
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Re: Effectiveness of public health measures

Post by shpalman » Fri Nov 19, 2021 9:45 am

F6.jpg
F6.jpg (104.32 KiB) Viewed 1458 times
(66) Bundgaard: https://doi.org/10.7326/M20-6817 (this is the "one randomized controlled trial")
(63) Doung-ngern: https://doi.org/10.3201/eid2611.203003
(43) Krishnamachari: https://doi.org/10.1016/j.ajic.2021.02.002
(36) Lio: https://doi.org/10.1186/s12889-021-10680-5
(60) Xu: https://doi.org/10.2196/21372
(57) Wang: https://dx.doi.org/10.1136/bmjgh-2020-002794
Mask wearing and covid-19 incidence—Six studies with a total of 2627 people with covid-19 and 389 228 participants were included in the analysis examining the effect of mask wearing on incidence of covid-19 (table 1) [36,43,57,60,63,66]. Overall pooled analysis showed a 53% reduction in covid-19 incidence (0.47, 0.29 to 0.75), although heterogeneity between studies was substantial (I2=84%) (fig 5). Risk of bias across the six studies ranged from moderate [36,57,60,66] to serious or critical [43,63].
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Re: Effectiveness of public health measures

Post by discovolante » Fri Nov 19, 2021 9:51 am

shpalman wrote:
Fri Nov 19, 2021 9:22 am
Well I also found it interesting that they did a meta-analysis of one study, but then it's also interesting that reviewer 2 seems to want to reject it but they publish it anyway with reviewer 2's comments as an editorial.

But that study involving more than 340,000 people in Bangladesh wasn't about mask wearing vs. non mask wearing, it was about telling people to wear masks and giving them free ones vs. not doing that.

https://www.poverty-action.org/sites/de ... 083121.pdf
All intervention arms received free masks, information on the importance of masking, role modeling by community leaders, and in-person reminders for 8 weeks. The control group did not receive any interventions.
The intervention increased proper mask-wearing from 13.3% in control villages (N=806,547 observations) to 42.3% in treatment villages (N=797,715 observations) (adjusted percentage point difference = 0.29 [0.27, 0.31]). This tripling of mask usage was sustained during the intervention period and two weeks after.
...
The proportion of individuals with COVID-like symptoms was 7.62% (N=13,273) in the intervention arm and 8.62% (N=13,893) in the control arm. Blood samples were collected from N=10,952 consenting, symptomatic individuals. Adjusting for baseline covariates, the intervention reduced symptomatic seroprevalence by 9.3% (adjusted prevalence ratio (aPR) = 0.91 [0.82, 1.00]; control prevalence 0.76%; treatment prevalence 0.68%). In villages randomized to surgical masks (n = 200), the relative reduction was 11.2% overall (aPR = 0.89 [0.78, 1.00]) and 34.7% among individuals 60+ (aPR = 0.65 [0.46, 0.85]). No adverse events were reported.
So that 9.3% reduction in symptomatic seroprevalence isn't coming from 100% mask wearing vs. 0% mask wearing, but rather 42.3% mask wearing vs. 13.3% mask wearing.
Do you know, I read the thread and almost assumed they must have been referring to a different study in Bangladesh because my recollection had also been that the large one that was reported was clear that mask uptake was far less than 100%. But I didn't check, so thanks.
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Re: Effectiveness of public health measures

Post by shpalman » Fri Nov 19, 2021 10:01 am

Well it has a slightly different title compared to that earlier preprint but I assume the same authors didn't do two of them.

Normalizing Community Mask-Wearing: A Cluster Randomized Trial in Bangladesh Abaluck et al. (what's the "Yale School of Management"?)

(link to the BMJ editorial: "the research on this is sh.t, here's an example" for convenience)
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Re: Effectiveness of public health measures

Post by Herainestold » Fri Nov 19, 2021 4:29 pm

So there is a real effect with a mask uptake of less than 100%.
It appears to be one of the better mask trials, but it needs to be replicated.
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Re: Effectiveness of public health measures

Post by Millennie Al » Sat Nov 20, 2021 2:32 am

I have briefly read through the part on masks and the studies it references. Below are my opinions on it, but the tl;dr is that the review is useless and the studies it cites are very weak or inapplicable. We wouldn't approve use of ivermectin because a survey of patients showed that those with better outcomes were more likely to have taken it, so we shouldn't accept it for other interventions either. Low quality studies, such as those which use self-reporting, should only be used as hints as to where to make proper investigations - not support for society-wide interventions.


36 Effectiveness of personal protective health behaviour against COVID-19.
doi:10.1186/s12889-021-10680-5

This is based on 24 patients with Covid-19 and 1113 people without.
The data on mask wearing is solely gathered through asking people
about what they did. It also shows that mask wearing is correlated
with other precautions.


43 The role of mask mandates, stay at home orders and school closure in curbing the COVID-19 pandemic prior to vaccination. doi:10.1016/j.ajic.2021.02.002

This does not study mask wearing at all - it compares legal measures
in the 50 states of the USA. It makes no allowance for people wearing
masks when not mandated or refusing to wear maks when mandated. Since
everything about Covid seems to be politicised (especially in the USA)
it is impossible to draw conclusions from such a simple study - even
about mask mandates rather than actual mask wearing.

57 Reduction of secondary transmission of SARS-CoV-2 in households by face mask use, disinfection and social distancing: a cohort study in Beijing, China.
https://www.bmj.com/lookup/ijlink/YTozO ... owOiIiO30=

This study looks a transmission with a household. There were 41
families where transmission occurred (infecting 77 people) and 83
families with no transmission. It relied on telephone interviews, so
suffers from the usual biases of that. Its conclusions are
interesting. The biggest risk factor was "Close contact at home >=
4 times" (OR=18.26 relative to no contact), followed by "Primary case
has diarrhoea" (OR=4.10) and Ventilation < 1 hour/day
(OR=2.55). Protective effects are found for "1 or more family members
(including primary case) wearing a mask at home before primary case's
illness onset date" (OR=0.21) and "Frequency of chlorine or ethanol based
disinfectant use for house cleaning" (OR=0.23 for once a day relative
to more rarely).


60 Relationship Between COVID-19 Infection and Risk Perception, Knowledge, Attitude, and Four Nonpharmaceutical Interventions During the Late Period of the COVID-19 Epidemic in China: Online Cross-Sectional Survey of 8158 Adults.
doi:10.2196/21372

Another self-reporting study. It also has this interesting bit:
"The reasons that we also included proper coughing habit as an end
point was that the habit may not only potentially reduce other
people’s risk of developing a COVID-19 infection but may also reduce a
person’s own risk through enhanced self-protection (eg, turning away
from those who did not practice proper coughing habit) or through
indirectly influencing other people’s coughing behavior as a role
mode". They don't define "proper coughing habit", but it seems obvious
that they have found evidence of some confounding (as the coughing and
infection refer to the same person).


63 Case-Control Study of Use of Personal Protective Measures and Risk for SARS-CoV 2 Infection
doi:10.3201/eid2611.203003

Yet another self-reporting study. This time 211 asymptonatic, infected
people and 839 uninfected people. It also includes correlation data
between different measures, showing that any relevant measure not
included would be quite likely to be correlated with the others, so
inflating their apparent effect.

66 Effectiveness of Adding a Mask Recommendation to Other Public Health Measures to Prevent SARS-CoV-2 Infection in Danish Mask Wearers: A Randomized Controlled Trial.
doi:10.7326/M20-6817

This one contains the magic word "randomised" which makes it better
than the others. It also does not rely on self-reporting.
Unfortunatly, it does not test mask wearing either. It tests the
difference between people told to wear a mask and people not told to
wear a mask. It then says:

"Results: A total of 3030 participants were randomly assigned
to the recommendation to wear masks, and 2994 were assigned
to control; 4862 completed the study. Infection with SARS-CoV-
2 occurred in 42 participants recommended masks (1.8%) and
53 control participants (2.1%). The between-group difference
was 0.3 percentage point (95% CI, 1.2 to 0.4 percentage
point; P = 0.38) (odds ratio, 0.82 [CI, 0.54 to 1.23]; P = 0.33).
Multiple imputation accounting for loss to follow-up yielded sim-
ilar results. Although the difference observed was not statistically
significant, the 95% CIs are compatible with a 46% reduction to
a 23% increase in infection."



I see I have been ninja'd by the BMJ as mentioned above, but their article has some different points, so well worth reading.

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Re: Effectiveness of public health measures

Post by shpalman » Sat Nov 20, 2021 7:49 am

Millennie Al wrote:
Sat Nov 20, 2021 2:32 am
I have briefly read through the part on masks and the studies it references. Below are my opinions on it, but the tl;dr is that the review is useless and the studies it cites are very weak or inapplicable. We wouldn't approve use of ivermectin because a survey of patients showed that those with better outcomes were more likely to have taken it, so we shouldn't accept it for other interventions either. Low quality studies, such as those which use self-reporting, should only be used as hints as to where to make proper investigations - not support for society-wide interventions...
Thanks for doing that, but how would you even test mask wearing as an intervention to the same standard as a drug trial? You obviously can't even blind it, let alone double-blind it. Should you give half the participants "fake" masks with holes in or missing layers of filtering material? That would be difficult to get ethical approval for since our starting point of view is that a bad mask means poor protection for the other people, not for you. That's why the interventions have to be decided at the whole community level, not the individual level.

Or, as someone will point out every so often, for lots of things we don't have an RCT.
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Re: Effectiveness of public health measures

Post by Millennie Al » Sun Nov 21, 2021 1:47 am

shpalman wrote:
Sat Nov 20, 2021 7:49 am
...how would you even test mask wearing as an intervention to the same standard as a drug trial? You obviously can't even blind it, let alone double-blind it. Should you give half the participants "fake" masks with holes in or missing layers of filtering material? That would be difficult to get ethical approval for since our starting point of view is that a bad mask means poor protection for the other people, not for you. That's why the interventions have to be decided at the whole community level, not the individual level.
Yes, it should use fake masks. They would have to be carefully designed so that the wearer is unable to distinguish them from real masks. To run such a study you would have to recruit a large number of participants (say 40,000 as that's what was used for approving the vaccines) and randomly assign them to two groups which differ only in the mask used (which will have to be supplied by the study, of course). The participants need to be trained in proper mask usage to ensure the clearest results. If the test is measuring protection of the wearer, that's sufficient. If it is testing protection of others, then a participant probably needs to be a household rather than an individual and the people need to routinely wear the masks at home. (It's difficult to think of another grouping of a small number of people which does not vary over the length of the study.

Ethical objections are effectively saying that we can't test masks because we already know they work. Since we don't know, those objections are invalid and ethical considerations demand that masks be properly tested as the world must have spent billions on masks during the pandemic and it is essential to know if this is value for money. Similarly, it is unethical to demand that people do something without having reasonable reasons to believe it is effective. In the case of masks that means that initially it's acceptable to mandate masks if it seems likely from what is already known that they might work, but it also means that there is a moral imperative for this to be a short-term emergency measure and proper testing must be started immediately.

The standard analogy of parachutes fails because parachutes are based on simple physics, which is completely understood to the extend needed to know that they work. Biology is vastly more complex and full of surprises.

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