HEPA filters are not particularly effective in filtering virus-sized particles. However, in my opinion, this is not particularly significant to this issue. Transmission may occur much more readily due to ingestion of airborne virus particles (aerosol droplets), person-to-person contact, and infected persons potentially contaminating contact surfaces that others are then in contact with.
Generally when these issues occur, the majority of mortalities are associated with elderly, very young and immuno-compromised persons, however there are usually small numbers of outliers that don’t fit into these groups. I commonly saw these patterns in a previous occupation.