Effects of Coronavirus Disease (COVID-19) Related Contact Restrictions in Germany, March to May 2020, on the Mobility and Relation to Infection Patterns

Abstract

In an effort to contain the spread of COVID-19, Germany has gradually implemented mobility restrictions culminating in a partial lockdown and contact restrictions on 22 March. The easing of the restrictions began 1 month later, on 20 April. Analysis of the consequences of these measures for mobility and infection incidence is of public health interest. A dynamic cohort of about 2,000 individuals in Germany aged 16-89 years provided individual information on demographic variables, and their continuous geolocation via a smartphone app. Using interrupted time series analysis, we investigated mobility by age, sex, and previous mobility habits from 13 January until 17 May 2020, measured as median daily distance traveled before and after restrictions were introduced. Furthermore, we have investigated the association of mobility with the number of new cases and the reproduction number. Median daily distance traveled decreased substantially in total and homogeneously across all subgroups considered. The decrease was strongest in the last week of March followed by a slight increase. Relative reduction of mobility developed parallel with number of new cases and the daily estimated reproduction number in the weeks after contact restrictions were implemented. The increase in mobility from mid-April onwards, however, did not result in increased case numbers but in further decrease. Other behavioral changes, e.g., wearing masks, individual distancing, or general awareness of the COVID-19 hazards may have contributed to the observed further reduction in case numbers and constant reproduction numbers below one until mid-July.

Keywords: COVID-19; Germany; SARIMA model; case numbers; contact restrictions; interrupted time series analysis; mobile tracking; mobility.

Figure 1

Median daily distances traveled between 13 January 2020 and 17 May 2020 stratified by three age groups (A), gender (B), and state (C). Dates of important governmental interventions in Germany are indicated with dashed vertical lines.

Figure 2

Observed median daily distances traveled (colored) by age group for the total period and simulated time series during the simulation period (black). Considered age groups were 16-29 years (A), 30-59 years (B), and 60 years and older (C).

Figure 3

Relative reduction of median daily distances between 9 March and 17 May, stratified by age group (A), gender (B), and previous mobility defined by distances traveled between 13 January and 8 March (C). Dates of important governmental interventions in Germany are indicated with dashed vertical lines.

Figure 4

Relative mobility reduction vs. reproduction number R (7-day value) from 6 March to 17 May 2020.