Skip to main content

Trends in COVID-19 Incidence After Implementation of Mitigation Measures – Arizona, January 22-August 7, 2020

Our take —

In Arizona, a spike in COVID-19 cases coincided with the relaxation of both a statewide stay-at-home order and business closures; daily case growth plateaued and was reversed following the introduction of local mask mandates, re-closure of non-essential businesses, and additional restrictions on restaurant dine-in capacity. Findings provide preliminary evidence for the risks of epidemic growth following phased re-opening, as well as the benefits of masking and other social distancing interventions to reduce COVID-19 incidence.

Study design


Study population and setting

The authors aggregated daily COVID-19 case counts in Arizona, as well as the 7-day moving average of daily COVID-19 cases, from March 11 to August 7, 2020. Daily COVID-19 case counts and 7-day moving averages were mapped onto implementation timelines for various COVID-19 control measures throughout the study period in order to examine potential effects of these interventions on COVID-19 incidence in Arizona. Implementation and phased liftings of the following mitigation measures were explored: restrictions on public gatherings (March 15), school and business closures (March 15 to 19), shelter-in-place ordinances (March 30), and mask mandates (June 17).

Summary of Main Findings

After the shelter-in-place ordinance was lifted, and business closures expired on May 15, 2020, Arizona recorded rapid growth in COVID-19 cases (151% increase in 7-day moving case average) between June 1 and 15th. After local mask mandates were introduced (June 17), businesses reclosed (June 29), and restaurants restricted dine-in capacity to 50% (July 9), average daily COVID-19 cases began declining in early July, falling 75% between July 13 and August 7th .

Study Strengths

The authors compared daily COVID-19 cases in Arizona over the study period to both the introduction and lifting of various mitigation measures designed to curb COVID-19 transmission.


While the authors identified temporal relationships between numerous mitigation measures and changing COVID-19 case counts, the extent to which changes in case counts can be attributed to the implementation and/or relaxation of these measures is uncertain. The introduction and lifting of these various policies, therefore, cannot be assumed to have caused these changes, given that other unmeasured variables (e.g., neighboring state policies, COVID-19 testing policies) with potential to impact COVID-19 incidence were not factored into the analysis. The analysis also did not assess adherence to policies and assumed that policies within Arizona and were implemented uniformly statewide.

Value added

This paper is among the first to explore COVID-19 epidemic dynamics following both the introduction and relaxation of various non-pharmaceutical interventions in the United States.

This review was posted on: 28 October 2020