HVAC upgrades...
...to support HEPA filtration would cost minimum 4 to. $8000 dollars for the air handler(depending on room size) plus installation. The filter would be about $150 to $250 each for the higher efficiency ratings and last up to 90 days. That's another $1000 a year, every year. Then you add the cost of the UV lighting plus installation and replace those lamps as they wear out and over 10 years you've spent at least $18000 to $24000 and you still wouldn't know if there was Covid in the ambient air. Standard air handlers can't cope with the added pressure drop associated w/HEPA filtration.