HEPA filtration works. We have known this for decades (below). They effectively filter out infectious aerosols in the correct (1-5 micron) size range (>99.9%). If you see "HEPA-like" (which always cost more) or other added bells and whistles (plasma/ionizers), DO NOT BUY!!(1/2) 
These don't help and can lead to worse air quality. Snake oil salespeople are coming out of the woodwork and stealing precious money from schools. It is a crime as they are taking advantage of schools who think "if we pay more, we better protect our kids". This is NOT true. (2/2)
HT @jmcrookston for digging up this old paper. There are literally hundreds of pubs on how well HEPA's work in reducing aerosol concentrations indoors. The good performance can be explained/predicted by basic physics. No RCT needed (end).
I am talking about standalone HEPA filtration. For central HVAC, MERV13 is recommended.
• • •
Missing some Tweet in this thread? You can try to
force a refresh
