Fig. 1

Fitted epidemic curves of COVID-19 case counts showing the impact of the mask mandate

Notes: Fitted epidemic curve of observed COVID-19 case counts, assuming a post-mandate mask effectiveness of 14.2%, and simulated epidemic curves assuming no mandate and continuation of pre-mandate mask effectiveness of either 7.2% or 11.2% (all three for the October 20 – December 20, 2021 period). The solid line is Illinois’s observed (fitted) cumulative COVID-19 case counts, and the broken lines are the simulated curves illustrating the cumulative total COVID-19 cases for the various scenarios that might have occurred if the mask mandate had not been enacted and mask efficacy was 20%. The differences between the solid and broken lines show the benefits of the mask mandate with greater divergence between the solid and broken lines indicating a greater impact. All results assume that the effects of nonpharmaceutical interventions —including masks—were constant over the two months shown