Early social distancing policies in Europe, changes in mobility & COVID-19 case trajectories: Insights from Spring 2020

Abstract

Background: Social distancing have been widely used to mitigate community spread of SARS-CoV-2. We sought to quantify the impact of COVID-19 social distancing policies across 27 European counties in spring 2020 on population mobility and the subsequent trajectory of disease.

Methods: We obtained data on national social distancing policies from the Oxford COVID-19 Government Response Tracker and aggregated and anonymized mobility data from Google. We used a pre-post comparison and two linear mixed-effects models to first assess the relationship between implementation of national policies and observed changes in mobility, and then to assess the relationship between changes in mobility and rates of COVID-19 infections in subsequent weeks.

Results: Compared to a pre-COVID baseline, Spain saw the largest decrease in aggregate population mobility (~70%), as measured by the time spent away from residence, while Sweden saw the smallest decrease (~20%). The largest declines in mobility were associated with mandatory stay-at-home orders, followed by mandatory workplace closures, school closures, and non-mandatory workplace closures. While mandatory shelter-in-place orders were associated with 16.7% less mobility (95% CI: -23.7% to -9.7%), non-mandatory orders were only associated with an 8.4% decrease (95% CI: -14.9% to -1.8%). Large-gathering bans were associated with the smallest change in mobility compared with other policy types. Changes in mobility were in turn associated with changes in COVID-19 case growth. For example, a 10% decrease in time spent away from places of residence was associated with 11.8% (95% CI: 3.8%, 19.1%) fewer new COVID-19 cases.

Discussion: This comprehensive evaluation across Europe suggests that mandatory stay-at-home orders and workplace closures had the largest impacts on population mobility and subsequent COVID-19 cases at the onset of the pandemic. With a better understanding of policies' relative performance, countries can more effectively invest in, and target, early nonpharmacological interventions.

Fig 1. Timeline of major COVID-19 policy interventions by country.

In response to the COVID-19 pandemic, European countries enacted a series of national policies intended to promote social distancing that varied across countries in terms of time (with respect to both calendar time and reported cases), nature, and enforcement (mandatory versus non-mandatory). Policy type is indicated with color and if that policy was instituted as a mandatory or non-mandatory policy is indicated with shape.

Fig 2. Relative change in mobility across study countries, Spring 2020.

Relative change in mobility in European study countries, as estimated using aggregated (anonymized with differential privacy) data from Google users who have opted-in to Location History. For each country, crosses indicate the date on which the 100th case was reported, squares indicate the date of the first mandatory social distancing policy, and triangles denote the date of shelter-in-place orders.

Fig 3. Linear relationship between relative change in mobility and change in case count.

Partial regression plot of the 2-week-lagged change in mobility showing the relationship between mobility and case counts. Note higher variation in the response given small changes in mobility. The x-axis represents residuals in the relative percent change in mobility and the y-axis represents residuals in the case count.