Estimated public health impact of concurrent mask mandate and vaccinate-or-test requirement in Illinois, October to December 2021

Table 2 Estimated cases and hospitalizations averted due to mask mandate for various levels of mask effectiveness^a

Mask Effectiveness, Pre-mandate^b	Mask Effectiveness, Post-mandate	Number of Cases Averted (Number of Hospitalizations Averted^c)
3.6%	6.1%	149,817 (3,028)
5.0%	6.1%	58,233 (1,177)
3.6%	7.1%	232,791 (4,705)
5.6%	7.1%	83,250 (1,683)
7.2%	12.2%	415,085 (8,390)
10.0%	12.2%	139,155 (2,813)
7.2%	14.2%	734,649 (14,849)
11.2%	14.2%	211,125 (4,267)
10.8%	18.3%	901,144 (18,214)
15.0%	18.3%	255,426 (5,163)
10.8%	21.3%	1,820,764 (36,801)
16.8%	21.3%	417,605 (8,441)

^aSee Appendix Table A1 for the Results from all 24 scenarios of combinations of pre-and post-mandate mask effectiveness
^bAssumes the levels of mask-wearing would have remained the same in the absence of the mask mandate
^cNumber of hospitalizations averted is calculated by multiplying the estimated number of averted cases by the infection-to-hospitalization ratio, which was assumed to be approximately 2.02% during that period [26]. Infection-to-hospitalization ratio is assumed not to vary with the assumed level of mask efficacy

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