Why the recent announcement by the CDC that masks do protect from COVID-19 should not surprise anyone.
Many people have claimed that masks cannot protect from COVID-19 because the pores in a mask are large enough for a virus particle to go through. The pores in an N95 filter are around 0.3 microns. A COVID-19 virus particle is typically between 0.06 to 1.4 microns.
Cloth masks have even larger pores. The pores in cloth masks are typically between 80 to 500 microns.
Since 0.06 microns is considerably smaller than 0.3 microns, many people claim that even an N95 mask cannot protect against COVID-19.
The CDC recently announced that masks protect both the wearers and those around them from COVID-19 and many people are surprised by this revelation. But I am not surprised. To me it is obvious.
When a person who has COVID-19 sneezes a number of droplets that may contain virus particles are propelled away from them. Those virus particles are not guided self-propelled missiles with advanced targeting and guidance systems that will seek out and fly through the 500 micron pore. They are ballistic projectiles.
The probability of a virus particle managing to make it through even a 500 micron pore is equivalent to the probability of someone armed with a hunting rifle hitting a golf ball from a quarter mile away. Perhaps a highly trained sniper could do it, but the chances are not very good.
And this assumes a single layer of fabric.
I have a PM2.5 mask that has a filter pocket and uses a filter. There are two layers of fabric and a multi-layer filter between me and the outside world. The probability that all the pores in these multiple layers will line up perfectly so that a virus particle expelled by a person standing six feet away from me sneezing is all but non-existent.
Thus simple logic should be enough to tell anyone that a mask, if properly worn, will significantly decrease the likelihood that you will infect someone when you cough or sneeze and decrease the likelihood that you will be infected.
As C-3PO put it in the movie Star Wars: Episode IV: A New Hope, “Sir. The possibility of successfully navigating an asteroid field is approximately 3,720 to 1”.