Significance Numerous COVID-19 studies used mobile phone data but with limited power in accounting for infection numbers. We have evaluated deidentified Global Positioning System (GPS) data from over 1 million devices in Germany and inferred contacts from coproximity of devices. Through calculating the contact graphs, we derived a contact index (CX) that exhibits a high correlation with the incidence-based reproduction number R so that changes in CX precede those in R by more than 2 wk. CX thus is an early indicator for outbreaks and can be used to guide social-distancing policies. Further questions, including those for the efficacy of vaccination, can be addressed with our method. We discuss limitations, e.g., transmission on international travel, and the relation to superspreading. Over the last months, cases of SARS-CoV-2 surged repeatedly in many countries but could often be controlled with nonpharmaceutical interventions including social distancing. We analyzed deidentified Global Positioning System (GPS) tracking data from 1.15 to 1.4 million cell phones in Germany per day between March and November 2020 to identify encounters between individuals and statistically evaluate contact behavior. Using graph sampling theory, we estimated the contact index (CX), a metric for number and heterogeneity of contacts. We found that CX, and not the total number of contacts, is an accurate predictor for the effective reproduction number R derived from case numbers. A high correlation between CX and R recorded more than 2 wk later allows assessment of social behavior well before changes in case numbers become detectable. By construction, the CX quantifies the role of superspreading and permits assigning risks to specific contact behavior. We provide a critical CX value beyond which R is expected to rise above 1 and propose to use that value to leverage the social-distancing interventions for the coming months.
【저자키워드】 COVID-19, Epidemiology, network science, 【초록키워드】 SARS-CoV-2, Efficacy, vaccination, social distancing, Infection, risk, Nonpharmaceutical interventions, Intervention, Transmission, heterogeneity, Germany, outbreak, International, Reproduction number, Travel, positioning, Critical, mobile phone, nonpharmaceutical intervention, Contact, individual, high correlation, construction, metric, over, limitations, System, country, effective, Cell, analyzed, identify, evaluate, detectable, evaluated, can be used, per day, changes in, expected, addressed, exhibit, recorded, statistically, Numerous, a metric, Significance, 【제목키워드】 Reproduction number, Contact, effective, the SARS-CoV-2,