Parent asked for evidence that mass mask wearing prevent the spread of the disease. You presented a study that shows some masks if worn properly block some viruses.

Can you see how the study you presented doesn't answer parent post's question?

Further, your study tests the first breath exhalation.

> We screened 3,363 individuals in two study phases, ultimately enrolling 246 individuals who provided exhaled breath samples (Extended Data Fig. 1). Among these 246 participants, 122 (50%) participants were randomized to not wearing a face mask during the first exhaled breath collection and 124 (50%) participants were randomized to wearing a face mask. Overall, 49 (20%) voluntarily provided a second exhaled breath collection of the alternate type.

So, your test says "when you put on a mask that mask will, immediately after you put it on, stop your exhaled breath hitting a plate placed in front of your mouth".

It says nothing about how effective that mask is over time.

Masks gets moist over time and virus will build up in it, are there any tests checking how well they work after a full workday? It wouldn't be strange if the virus buildup on the mask pretty quickly makes you start spreading covid, and then the false sense of security would actually cause them to increase spread rather than reduce it.

Edit: Also that is for surgical face masks, most people just put a piece of cloth in their face. I would like to see a study for a piece of cloth in front of your mouth for the entire day and see how much virus there is after that.

Thanks. That study doesn't measure any sort of disease spread. It measures the density of candle smoke on either side of the mask.

Not at all, perhaps you meant another commenter? From the link "Before exhaled breath collection, each participant was randomly allocated in a 1:1 ratio to either wearing a surgical face mask (cat. no. 62356, Kimberly-Clark) or not during the collection. [...] Participants were then invited to provide a second exhaled breath sample of the alternate type (for example if the participant was first assigned to wearing a mask they would then provide a second sample without a mask)"

They actually tested infected patients with and without mask.

>We detected coronavirus in respiratory droplets and aerosols in 3 of 10 (30%) and 4 of 10 (40%) of the samples collected without face masks, respectively, but did not detect any virus in respiratory droplets or aerosols collected from participants wearing face masks, this difference was significant in aerosols and showed a trend toward reduced detection in respiratory droplets (Table 1b).

This study is incredibly small, and operating on the limits of significance. Its hardly conclusive, and was done under fairly extreme conditions (30 mins in close proximity) compared to the scenarios in which masks are mandated today. The authors even mention that, for those who did not cough, no detectable virus was identified regardless of whether a mask was worn. Considering that the point of mandatory masking is to prevent asymptomatic transmission from brief interactions with strangers, I just don't find this study very convincing as a scientific basis for a mask mandate.

> Participants were recruited year-round from March 2013 through May 2016

The study you linked did not have any covid patients.

The question was

> slows the spread of COVID-19 or a similar respiratory disease

What makes you believe that COVID-19 is spread significantly differently that the inconvenience of having to wear a mask is not bearable relative to the potential benefits? Do you believe that masks have risks other than being inconvenient?

fwiw: my household’s being hyper-vigilant regarding covid, rarely doing anything beyond social distancing. i'm looking for a study that validates the conventional wisdom about masking so that we know we aren’t contributing to the spread. at no point am i suggesting any behavior that isn’t backed by scientific data.

They did have coronavirus patients, though. I'm not aware of significant physical differences between Covid-19 and other coronaviruses.