I found this at the New York Times. If this idea is true, it would be a good thing.

Is your mask helping you build immunity?

As the world awaits a coronavirus vaccine, a team of researchers has come forward with a provocative new theory: Masks might act as a crude vaccine.

Some experts are intrigued by the idea that if a small number of pathogens slip through the mask, they might prompt the body to produce immune cells that can remember the virus and stick around to fight it off again.