The parts we do know aren't exactly reassuring, but they're limited to the physical properties of masks (i.e. do they stop aerosols / particles). It's somewhat

The parts we do know aren't exactly reassuring, but they're limited to the physical properties of masks (i.e. do they stop aerosols / particles). It's somewhat hard to test how big an effect they have on preventing infections since it's nigh impossible to control the other variables (ethically).