2024 Yes https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0291840 Zand, Martin S. North America Epidemiology Study Teachers Students Carbon Dioxide (CO2) Ventilation rates COVID rates 97% of rooms had an estimated ACH ?4.0, with 7% having CO2 levels ?2,000 ppm for up to 3 hours per school day. A statistically significant correlation was found between the time that a room had CO2 levels ?1,000 ppm and SARS-CoV-2 PCR tests normalized to room occupancy, accounting for 43% of the variance. No statistically significant correlation was found for room ACH and per-room SARS-CoV-2 cases. Rooms with ventilation systems using MERV-13 filters had lower SARS-CoV-2-positive PCR counts. These findings led to ongoing efforts to upgrade the ventilation systems in this community-engaged research project.