Importance: As states reopened their economies state and local officials made decisions on policies and restrictions that had an impact on the evolution of the pandemic and the health of the citizens. Some states made the decision to lift mask mandates starting spring 2021. Data-driven methods help evaluate the appropriateness and consequences of such decisions.
Objective: To investigate the association of lifting the mask mandate with changes in the cumulative coronavirus case rate.
Design: Synthetic control study design on lifting mask mandate in the state of Iowa implemented on February 7, 2021.
Setting: Daily state-level data from the COVID-19 Community Profile Report published by the US Department of Health & Human Services, COVIDcast dataset of the Delphi Research Group, and Google Community Mobility Reports.
Exposures and Outcome: Mask mandate policy lift at the state level. State-day observations of the cumulative case rate measured as the cumulative number of new cases per 100,000 people in the previous 7 days.
Results: The cumulative case rate in Iowa increased by 20%–30% within 3 weeks of lifting the mask mandate as compared with a synthetic control unit. This association appeared to be related to people, in fact, reducing their mask-wearing habits.
Conclusions: Lifting the mask mandate in Iowa was associated with an increase in new COVID-19 cases. Caution should be applied when making this type of policy decision before having achieved a more stable control of the pandemic.