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**Hugh** · 22-07-2021, 14:35

Quote:

Originally Posted by Pierre

The bottom line is, the evidence of the effectiveness of masks is flimsy and always has been.

In combination with other measures, the science shows masks reduce infection.

https://science.sciencemag.org/content/372/6549/1439

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Face masks effectively limit the probability of SARS-CoV-2 transmission

https://www.ucsf.edu/news/2020/06/41...-masks-prevent

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Still Confused About Masks? Here’s the Science Behind How Face Masks Prevent Coronavirus

There are several strands of evidence supporting the efficacy of masks.

One category of evidence comes from laboratory studies of respiratory droplets and the ability of various masks to block them. An experiment using high-speed video found that hundreds of droplets ranging from 20 to 500 micrometers were generated when saying a simple phrase, but that nearly all these droplets were blocked when the mouth was covered by a damp washcloth. Another study of people who had influenza or the common cold found that wearing a surgical mask significantly reduced the amount of these respiratory viruses emitted in droplets and aerosols.

But the strongest evidence in favor of masks come from studies of real-world scenarios. “The most important thing are the epidemiologic data,” said Rutherford. Because it would be unethical to assign people to not wear a mask during a pandemic, the epidemiological evidence has come from so-called “experiments of nature.”

A recent study published in Health Affairs, for example, compared the COVID-19 growth rate before and after mask mandates in 15 states and the District of Columbia. It found that mask mandates led to a slowdown in daily COVID-19 growth rate, which became more apparent over time. The first five days after a mandate, the daily growth rate slowed by 0.9 percentage-points compared to the five days prior to the mandate; at three weeks, the daily growth rate had slowed by 2 percentage-points.

https://www.pnas.org/content/118/4/e2014564118

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Conclusion

Our review of the literature offers evidence in favor of widespread mask use as source control to reduce community transmission: Nonmedical masks use materials that obstruct particles of the necessary size; people are most infectious in the initial period postinfection, where it is common to have few or no symptoms (45, 46, 141); nonmedical masks have been effective in reducing transmission of respiratory viruses; and places and time periods where mask usage is required or widespread have shown substantially lower community transmission.

The available evidence suggests that near-universal adoption of nonmedical masks when out in public, in combination with complementary public health measures, could successfully reduce R to below 1, thereby reducing community spread if such measures are sustained.