In the first few weeks of Covid-19, when masks were optional, we had close to a hundred staff at our hospital get sick with the disease. In the months since masks were made mandatory, we've had less than a dozen staff get sick.

You haven't seen data on filtration size because most journalists fall out of their chairs in boredom when looking through technical data. The virus (which is about .125 microns) is filtered out very well, despite its small size. Take a look at page 5 here: https://www.docdroid.net/Xdh8K6O/

Even if these journalists wanted to find it, they'd have a tough time right now, because so many sites are whitewashing their information with feel good WHO/CDC/Google approved versions of prior information.

The current (April 4,2020) 3M page for this technical bulletin omits some this.

Here's 3M's explanation of how tiny viruses are filtered out by masks with pores that are much larger than the virus:

Many particulate respirators use a non-woven fibrous filter media to capture particles. Fibers from less than 1 μm to 100 μm in size crisscross to form a web of many layers which is mostly air due to the spaces between the fibers. It is these spaces between fibers that allow for breathability. Particles are trapped, or captured, when flowing through the layers of filter media, and a particle becomes attached to a fiber due to a number of different mechanisms. The most common of these are gravitational settling, inertial impaction, interception, diffusion, and electrostatic attraction.

To understand how a particle is captured, one must first consider the movement of air through the filter media. The path of the air around a fiber may be described in terms of imaginary streamlines. Any particle carried by the air may or may not stay within the streamlines depending largely upon the particle's size (aerodynamic diameter).Very large particles (< 100 μm) in slow moving airstreams may settle out due to gravity. However, most respirable particles are too small for this mechanism. Respirable particles above 0.6 μm in diameter are typically captured efficiently by interception and inertial impaction.21 Inertial impaction occurs when a particle cannot follow an air streamline around a fiber because of its inertia and instead impacts into the fiber. In the interception mechanism, the particle holds to the streamline, but that streamline will naturally bring the particle close enough to come in contact with the fiber. In contrast, diffusion is typically very efficient for particles smaller than 0.1 μm. Random movements of air molecules collide with these very small particles and cause them to wander across streamlines until they come in contact with a fiber.Because of the various mechanisms by which particulate filtration occurs, the smallest particles are typically not the most difficult to filter. Most particulate filters have a region of lower filtration efficiency somewhere between 0.05-0.5 μm.1 Particles in this range are large enough to be less effectively pushed around by diffusion, but small enough to be less effectively captured by interception or impaction. The most penetrating particle size (MPPS) will depend on the filter media, air flow, and electrostatic charge on the particle. Filters that use electrostatic attraction may have a MPPS shifted to a slightly smaller size range.Filtration efficiencies of six different commercially available US N95 filtering facepiece respirators as tested by 3M are shown in the left side of Figure 1. (Previous research has shown that for 3M products, European FFP2 respirators have equivalent or better filtration efficiency in tests representative of health care environments.) Averaged filtration efficiencies are shown as a function of different sized sodium chloride particles at a flow rate of 85 liters per minute.

Fig -1 https://i.imgur.com/OrXS8sB.png