[Billthedrill]

Yep - some HEPA filters go down to .3 microns, but that's still too large to get virii. Not that you have to - if you manage to filter out the droplets the virii are riding, you're fine. .3 microns is small enough for most bacteria.

[Nebullis]

The danger (if any) is from the person sitting right in very close proximity to you. It doesn't matter if the air is outside air or recirculated air.