Yeah it's strange. Air sterilizing and air purifying is different.
This thread is air purification meaning taking the dust out from the air. Anti microbial don't dissolve air particles ya?
HEPA filters are perfectly capable of filtering (1) bacteria, they are really big (2) viruses spread via airborne infection on a nuclei, eg sneeze/cough aerosolised droplets. These droplets are much bigger than the viruses themselves.
And (3) Quite a number of viruses as well, but a sigle viruses(eg RNA material) really do not float in the air by themselves. They agglomerate or in the example of influenza, the droplet nuclei is several microns.
(you can google on the use of N95 and prevention of influenza, got several research studies done stating that does filters extremely well for wearers)
HEPA filters do operate below 0.3 microns. That is just the MPPS or Most Penetrating Particle Size. They do this by the diffusion effect. eg Samsung AX40 or AX60 filters are tested to be 99% efficient as well at 0.1 microns.
HEPA filters are used in infectious diseases isolation rooms, like SARS, MERS-CoV. Just a matter of different grading/quality. But they do work around the same ballpark and same principle.
Lastly, the manufacturers do test the filtration performance against various HxNx viruses. Eg Samsung/Sharp.
But it is true that some agglomerated viruses are still extremely small and their infectious "dosage" is very low. But for the influenza viruses that we are concerned with spread via aerosolised coughs, sneeze, they are captured very verywell with HEPA. In a healthcare setting, some procedures like intubation generates a good amount of aerosols. Hence needing negative pressure rooms, HEPA filtration, N95/N99/N100 and PPEs.
