Mask studies have been done for decades. In the majority of the studies looking at influenza, the cloth and medical masks offer little protection. They do block some sneezing or coughing droplets from being expelled though, some.
Some data has been collected for mask effectiveness with respect to SARS-CoV-2. N95 masks do better than cloth or medical masks. But medical and cloth masks don't offer significant protection compared to not wearing them. However, this is for one-way protection from the person wearing it.
The push for mask-wearing now is said to be that it stops people who are sick, or alleged asymptomatic people, from coughing or sneezing out droplets into the air and lingering long enough as someone walks by to pick them up before they drop down to a surface or get blown by the wind. One issue I have with this is that if you're asymptomatic you aren't going to be coughing or sneezing, since those are symptoms. Anyways.
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It would be good to do randomized controlled trials (RCTs) for COVID infection and mask prevention, like has been done before with influenza. There is a problem with that, Dr. Fauci opposes it.
Fauci spoke with students at Georgetown University’s Institute of Politics and Public Service on July 14. He was asked about doing new studies on masks:
"What kind of studies can we do right now in the middle of the pandemic about masks and transmission of the disease? Or are we just relying on anecdotal evidence because we are not able to do those kind of studies right now?”
Sounds reasonable. Studies vs. anecdotes about how effective they are. But Fauci doesn't want to go for study. He says it's unethical to have people not wear face masks, "because that would mean having people not wear masks and see if they do better." Therefore, no new studies can be done. Convenient.
“Right now, I’m convinced enough in the summation and totality of the data that has been analyzed by meta-analysis that … the benefit of wearing a mask clearly is there and is better than not wearing a mask.”
Is this because he knows of the previous data, and the new data would be the same, so it's better to just tout "new analyses of previous data" shows how effective masks are?
There are recent meta-review analyses published in May. One from the CDC, and another in Travel Medicine and Infectious Disease. They come to different conclusions:
The CDC concludes:
In this review, we did not find evidence to support a protective effect of personal protective measures or environmental measures in reducing influenza transmission.
The other states:
Meta-analyses suggest that mask use provided a significant protective effect.
I haven't looked at each of the studies used in the meta-reviews. Given the size of SARS-CoV-2 is 0.125 microns, which is much smaller than the pores of a cloth or medical mask, they don't offer complete protection from SARS-CoV-2 if it's alone in the air. N95 masks only filter 0.3 microns and above. But if the alleged virus is moving in water droplets, then it can be trapped by the mask. Not that is definitely will, but it can. It can also go through, and around the sides, top and bottom of the mask where air is also coming and going from.
Masks are not without health issues. Breathing issues, chest discomfort or pain and headaches is not uncommon to be experienced. Someone driving with an N95 mask passed out and hit a post last week. Oxygen gets reduced, and carbon dioxide increases.