New study on HEPA air cleaners in Finnish school study. Kids fill in daily diary of respiratory symptoms and the prevalence of symptoms reduced when the air cleaner was on. However the prevalence also decreased when the air cleaner was on but HEPA removed 🧵

6 schools and 27 classrooms under baseline, air cleaner off, HEPA on and SHAM (air cleaner on but no HEPA filter). Air cleaners also included activated carbon to remove TVOC. If kids had symptoms they scored these, air cleaner reduces symptom severity with and without HEPA