I am a PE for a large commercial/Industrial ventilation company. Not only do we manufacture and sell billions in product but our owner has private schools. Our research in general ventilation has made sense also. Normal restaurant/ school ventilation is recirculating air at about a 80% clip. Using 100% conditioned out side air with constant air changes we have had 4 confirmed cases in the schools (6 schools, about 1200 students plus teachers/staff). Basic premise, do not recirculate contaminated air...makes sense and why it is always the standard in clean hospital rooms. Issues...mostly cost, but done right the cost is minimal compared to standard HVAC systems. Just what I know and do daily