Accross 144 classrooms in 31 schools air measurements reveal that, even with mechanical ventilation in place, improved airflow reduces illness related absences (IRA).
“The annual illness-related absence rate at the classroom level was extracted from the student-level absence data and regressed on measured indoor environmental parameters. Significant associations were found. Every 1 L/s per person increase in ventilation rate decreased the annual absence rate by 5.59 days, corresponding to a 0.15% increase in the average daily attendance rate, while every additional 1 μg/m3 of indoor PM2.5 was associated with an increased annual absence rate of 7.37 days, corresponding to a 0.19% increase in average daily attendance rate.”