N95 filters at least .3 microns. Covid on its own is .125 microns. But covid doesnt generally float on its own. Its bonded to stuff like respiratory droplets (~50 microns) whose larger size is filterable.
As a barrier, N95 masks and higher can reduce, if not outright block. Viral load is a key element in how sick one gets and how body reacts to build defenses.
General surgical masks and cloth masks on the other hand only act as direct splash guards and serve the same purpose as a diaper, but made for the face. KN95 masks or any that fold are not suitable for prevention.
