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Timing of Community Mitigation and Changes in Reported COVID-19 and Community Mobility – Four U.S. Metropolitan Areas, February 26-April 1, 2020

Our take —

Local, state, and national policies designed to encourage physical distancing preceded substantial but variable reductions in the percentage of residents leaving home each day in New York, San Francisco, Seattle, and New Orleans. The marginal impacts of these policies on adherence to physical distancing, and consequently to SARS-CoV-2 transmission, remain unquantified.

Study design

Ecological

Study population and setting

The study considered four United States metropolitan areas with high COVID-19 burdens (Seattle, San Francisco, New Orleans, and New York City) between February 26 and April 1, 2020. Authors assessed temporal relationships among co-occurring local, state, and national declarations (e.g., stay-at-home and shelter-in-place orders, restrictions on mass gatherings, school/business closures, the White House “15 Day” Plan) and the uptake of physical distancing recommendations via a measure of community mobility (% leaving home per day) generated from aggregated samples of mobile device data. These temporal trends were examined alongside trends in COVID-19 case counts.

Summary of Main Findings

Although policy announcements occurred at different stages of epidemic trajectories (as determined by cumulative COVID-19 cases) across metropolitan areas, the announcements preceded notable reductions in the percentage of residents leaving home each day in all four cities between February 26 and April 1 (from ~80% in all four areas to 42% in New York, 47% in San Francisco, 52% in Seattle, and 61% in New Orleans).

Study Strengths

Specific policy communications were disaggregated by ecological level of enforcement (e.g., local, state, or national) and implementation date. The community mobility metric is a reasonable proxy for uptake of social isolation recommendations.

Limitations

Temporal relationships between physical distancing policies and community mobility are purely descriptive and unquantified, thereby constraining inference. Disaggregation of policies by implementation setting and announcement date might permit estimation of specific policy effects, but no such attempt is made. The community mobility metric employs mobile device activity from 3.6 – 6.4% of the total population in these four cities, and no information about characteristics of mobile device users is available; it is not clear how representative these results may be. Finally, results may not be generalizable to other U.S. settings.

Value added

This is among the first studies to disaggregate and descriptively analyze temporality in the implementation of multiple physical distancing policies at local, state, and national levels with individual mobility in the United States.