Alliance for Pandemic Preparedness

October 30, 2020

Association of County-Wide Mask Ordinances with Reductions in Daily CoVID-19 Incident Case Growth in a Midwestern Region Over 12 Weeks

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  • [Pre-print, not peer-reviewed] Missouri counties with mask mandates had a daily percent COVID-19 growth rate that was 32% lower than the growth rate in counties without mask mandates, based on a population-based quasi-experimental longitudinal study conducted from June to September. In the 3 weeks before mandatory mask mandates were instated, the average daily percent increase in incident COVID-19 cases was similar across all counties (0.9% vs. 1.3%). At 12 weeks post-mask mandate, the average daily COVID-19 case growth in counties with no mandate was 2.4%, which was significantly higher than the average daily COVID case growth among counties with a mandate (1.4%). Following implementation of mask mandates, disparities in infection rate by race and population density were no longer significant.

Shacham et al. (Oct 30, 2020). Association of County-Wide Mask Ordinances with Reductions in Daily CoVID-19 Incident Case Growth in a Midwestern Region Over 12 Weeks. Pre-print downloaded Oct 30 from https://doi.org/10.1101/2020.10.28.20221705