These are observation studies, some web based, some self reporting, some better than those. Observation studies are the lowest level of "scientific" studies and generally can't provide causation. That means you can't separate mask wearing from other mitigation efforts and natural decay in the community. The spread charted looks like serial bell curves, with an upside and downside for the spread. No attempt was done to place the time period of the study onto the bell curve of the spread, so no way to separate out natural decay of the spread. The fact that the CDC still is reporting the Hair Salon "study" and the Kansas study as proof demonstrates how badly they want people to wear masks. Both these studies are laughably bad. The USS Roosevelt study was "self reporting" on an aircraft carrier.
What is excluded are 50 years of studies on viral respiratory spread, many of which are controlled random trials (RCTs) which indicate mask wearing have no statistical significance. Example of these were a 2016 study Macintyre et al. and a 2010 study Canini et al. which showed no improvement in source control (wearing masks benefits others). There are multiple studies Lawson et al (2010) that demonstrates that hand hygiene is effective and when done in concert with masks provide no further mitigation. A CDC funded study Cowling et al 2009, found that hands only group did better than the hands plus mask group, but not statistically significant in a large multi-variate study. Summarizing the CDC funded study, Canini writes that “no additional benefit was observed when facemask [use] was added to hand hygiene by comparison with hand hygiene alone.”
There has been one RCT study looking at masking and Covid spread, the Danish study; Bundgaard 2020. The study found that 1.8 percent of those in the mask group and 2.1 percent of those in the control group became infected with Covid-19 within a month, with this 0.3-point difference not being statistically significant.
Just listing a bunch of observation studies isn't proof of anything. Certainly doesn't overturn 50 years of studies on the topic. And by not listing studies that both a higher level of scientific evidence and providing evidence against your public stance, the CDC proves it is more about propaganda than science.
