Thread by @ReformedTrader

1/ Global Assessment of the Impact of Masking on COVID-19: A Country Level Comparative and Retrospective Analyses Using the Richards Model (Mamun, Vejerano)

"Laboratory and modeling studies did not translate to a measurable difference in the real world."

europepmc.org/article/ppr/pp…

2/ "We are unaware of studies assessing masks’ effectiveness using real cases from multiple countries.

"The filtration efficiency of ordinary surgical (~12%) or cloth-based masks (~10%) is inferior to high-efficiency masks (≥95%). Aerosol leakage is also higher due to poor fit.

3/ "The Richards model can reasonably estimate the time when a phase shift occurs during an outbreak (turning point, ti), the infection rate (r), the exponential nature of the epidemic (α).

"It applies best for a curve consisting of a single high peak and a turning point."

4/ "Figure 2 is the map of the weekly infection rate. Countries like Faroe and Falkland Islands have yielded higher rates (1.71 and 2.24, respectively). We attribute this to an earlier turning point and a lower infection load compared to densely populated areas."

5/ "For North America, infection rates are higher for countries with a mask mandate than without masks."

NOTE: Here and in the figures that follow, it's possible that there are confounding variables involved.

6/ "Figure 4 is the map of the curve steepness in different countries. In North America, both mean and median α were higher for without mask-wearing countries. Comparison of α between countries with and without a mask mandate is depicted in the box plot in Figure 5."

7/ "Comparison of turning points between countries with and without a mask mandate across different regions is depicted in the box plot in Figure 7."

8/ "The sharp rise of COVID-19 infection cases amidst various public health interventions has led many countries to declare a national mandate on public masking. The conflicting result in the scientific literature and media outlets confound widespread adoption of masking."

9/ "But people wear masks imperfectly and inconsistently.

"The growth and dynamics of a pandemic are inextricably complex due to numerous variables, rendering prediction challenging.

10/ "We found no significant differences with r, a, and ti (Figures 3, 5, 7) between countries that did/did not mandate mask-wearing.

"A simple correlation analysis suggests that an early mask mandate did not result in a shorter turning point of country-specific COVID-19 cases."

11/ "The success in Bangladesh, Hong Kong, and Singapore cannot be generalized, potentially due to cultural, behavioral, and other factors that are difficult to identify.

12/ Caveats:

"Unawareness of airborne transmission may have driven the rise in cases despite masking mandates.

"Our analysis cannot disentangle the impact of other NPIs. It should also be interpreted within the context that data were acquired during the pandemic's early phase."

13/ "In general, laboratory and modeling studies on masks’ effectiveness did not translate to a measurable difference in the real world due to behavioral and other factors. Early masking mandates did not result in a shorter turning points of country-specific COVID-19 cases."

14/ Effectiveness of three versus six feet of physical distancing among primary and secondary students and staff


First Literature Review: Lockdowns Only Had a Small Effect on COVID-19


Lockdown Cost/Benefits

15/ Comments:

The results are compatible with masks working but mask _mandates_ not working.

This distinction has intuitive and empirical support. For example, Herby finds that mandated restrictions add little or no benefit voluntary changes in behavior:

16/ It's also possible that mandates are positively correlated with subsequent case growth.

Experts and policymakers don't have a great predictive track record (see below), but it would still be useful to see what effect, if any, this might have had.

17/ Bendavid et al. distinguish between less-restrictive and more-restrictive mandates. They find some potential benefit to less-restrictive measures (though controlled experiments need to be done to be sure) and no benefit to more-restrictive measures.