Characterizing collective physical distancing in the U.S. during the first nine months of the COVID-19 pandemic

The COVID-19 pandemic offers an unprecedented natural experiment providing insights into the emergence of collective behavioral changes of both exogenous (government mandated) and endogenous (spontaneous reaction to infection risks) origin. Here, we characterize collective physical distancing—mobility reductions, minimization of contacts, shortening of contact duration—in response to the COVID-19 pandemic in the pre-vaccine era by analyzing de-identified, privacy-preserving location data for a panel of over 5.5 million anonymized, opted-in U.S. devices. We define five indicators of users’ mobility and proximity to investigate how the emerging collective behavior deviates from typical pre-pandemic patterns during the first nine months of the COVID-19 pandemic. We analyze both the dramatic changes due to the government mandated mitigation policies and the more spontaneous societal adaptation into a new (physically distanced) normal in the fall 2020. Using the indicators here defined we show that: a) during the COVID-19 pandemic, collective physical distancing displayed different phases and was heterogeneous across geographies, b) metropolitan areas displayed stronger reductions in mobility and contacts than rural areas; c) stronger reductions in commuting patterns are observed in geographical areas with a higher share of teleworkable jobs; d) commuting volumes during and after the lockdown period negatively correlate with unemployment rates; and e) increases in contact indicators correlate with future values of new deaths at a lag consistent with epidemiological parameters and surveillance reporting delays. In conclusion, this study demonstrates that the framework and indicators here presented can be used to analyze large-scale social distancing phenomena, paving the way for their use in future pandemics to analyze and monitor the effects of pandemic mitigation plans at the national and international levels.Author summary: The COVID-19 pandemic resulted in some of the most significant disruptions to collective human behavior. In this study, we quantified the nature and scale of these disruptions during the first nine months of the pandemic by estimating changes in daily routines related to mobility, commuting, and social contacts. We used high-resolution mobility data that describe the physical movements of over 5.5 million individuals in the United States. Our findings indicate that the strength of the behavioral responses varied during different phases of the pandemic, across locations (states and cities), and across social settings (urban versus rural). We also found that reductions in commute flows were correlated with employment characteristics and that our proposed indicators for social interactions could be used as early warnings of potential future negative health outcomes (e.g., new daily deaths), thus opening up the possibility of using these metrics as additional situational awareness tools in future outbreaks.