Thanks, better than nothing, I guess. HEPAs are good to 0.3 micrometers, while Coronaviruses are about 0.12 micrometers (120 nanometers). So they will get bacteria and other single cell microbes, which are over 1 micrometer, but not nearly as many virus particles. Understandable - they’ve never had to deal with anything like Coronavirus in the past.
As to how they operate and recirculate air, that’s actually up to the airline. Back when I was in the business, we were putting in additional recirculation fans due to airline demand (less fresh air, less fuel burn). I don’t think it’s as bad now, or at least it’s not in the news as much (and perhaps there actually are regulations requiring the 50% fresh air as the article states...there weren’t before). I actually don’t know, but I sure as heck don’t want people here thinking it’s safe to fly with this virus bouncing around, unless we’re sure that’s true.