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Association of State-Issued Mask Mandates and Allowing On-Premises Restaurant Dining with County-Level COVID-19 Case and Death Growth Rates – United States, March 1-December 31, 2020

Our take —

This ecological study on the impact of SARS-CoV-2 mitigation measures in the US found that county-level case and death daily growth rates declined following the implementation of mask mandates and increased following restaurant reopenings. However, due to several key limitations in the study design and statistical analyses, results from this study should be interpreted very cautiously.

Study design

Ecological

Study population and setting

The study used county-level data on SARS-CoV-2 cases and deaths as well as the implementation dates of mask mandates and on-premise dining reopenings to evaluate the impact of masks mandates and restaurant reopenings on subsequent SARS-CoV-2 spread and mortality in the US. Dates of policy implementation were extracted from state and county websites, while case and death data were extracted from state and county public health department websites. Primary outcomes included daily growth rates for cases and deaths, which were estimated as the change in log cases or deaths from the previous day.

Associations between mask mandates and restaurant reopenings with the primary study outcomes were estimated using weighted least squares regression, and were assessed 20 days within implementation as well as 21-40 days, 41-60 days, etc. through 100 days following implementation. Associations between mitigation measures and outcomes in the pre-implementations periods were also examined. Models included adjustment for bar closures, stay-at-home orders, gathering size limitations, daily testing rates, county fixed effects, and day.

Summary of Main Findings

This study found that mask mandates, which were implemented in 75% of US counties, were associated with lower daily case and death growth rates (0.5 and 0.7 percentage point daily decrease within 1 to 20 days after implementation, respectively; p<0.001) following their passage. While counties allowing for reopening of on-premises dining (98% of all counties) did not experience an initial rise in cases within the first 40 days, they did experience a significant increase in both the daily growth rates of cases by 41 days and deaths by 61 days after reopening (p<0.001 for both).

Study Strengths

Data used for this study were gathered directly from primary sources (i.e., local government websites).

Limitations

There were several major limitations to this study. First, there were numerous SARS-CoV-2 mitigation policies implemented over the same calendar timeframes as mask mandates and restaurant restrictions/reopenings, and it is unclear why the impacts of only two of a large number of county-level mitigation measures were assessed in this study. Relatedly, while the authors controlled for several mitigation measures that may have confounded associations between mask mandates and restaurant restrictions with daily changes in cases and deaths, it is unclear whether all mitigation measures implemented within counties were actually included in the analysis and the extent to which those mitigation measures included temporally overlapped with one another: substantial overlap (i.e., statistical collinearity) would likely impact meaningful estimation of exposure effects. Third, cases and death rates change over time due to infectious disease dynamics, which were not accounted for in the analysis. Fourth, and perhaps most critically, authors controlled for daily testing rates in their adjusted models. Testing rates are arguably a proxy for case rates, one of the two primary study outcomes, thus potentially rendering effect estimates from the case rate models uninterpretable. Lastly, the primary outcomes were based on daily reported changes in cases and deaths, which are likely subject to extreme variations due to reporting/surveillance biases.

Value added

This study contributes to a large body of ecological studies examining the impacts of SARS-CoV-2 mitigation measures on virus associated cases and deaths.

This review was posted on: 26 March 2021