TY - JOUR T1 - The mobility gap: estimating mobility thresholds required to control SARS-CoV-2 in Canada JF - Canadian Medical Association Journal JO - CMAJ SP - E592 LP - E600 DO - 10.1503/cmaj.210132 VL - 193 IS - 17 AU - Kevin A. Brown AU - Jean-Paul R. Soucy AU - Sarah A. Buchan AU - Shelby L. Sturrock AU - Isha Berry AU - Nathan M. Stall AU - Peter Jüni AU - Amir Ghasemi AU - Nicholas Gibb AU - Derek R. MacFadden AU - Nick Daneman Y1 - 2021/04/26 UR - http://www.cmaj.ca/content/193/17/E592.abstract N2 - BACKGROUND: Nonpharmaceutical interventions remain the primary means of controlling severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) until vaccination coverage is sufficient to achieve herd immunity. We used anonymized smartphone mobility measures to quantify the mobility level needed to control SARS-CoV-2 (i.e., mobility threshold), and the difference relative to the observed mobility level (i.e., mobility gap).METHODS: We conducted a time-series study of the weekly incidence of SARS-CoV-2 in Canada from Mar. 15, 2020, to Mar. 6, 2021. The outcome was weekly growth rate, defined as the ratio of cases in a given week versus the previous week. We evaluated the effects of average time spent outside the home in the previous 3 weeks using a log-normal regression model, accounting for province, week and mean temperature. We calculated the SARS-CoV-2 mobility threshold and gap.RESULTS: Across the 51-week study period, a total of 888 751 people were infected with SARS-CoV-2. Each 10% increase in the mobility gap was associated with a 25% increase in the SARS-CoV-2 weekly case growth rate (ratio 1.25, 95% confidence interval 1.20–1.29). Compared to the prepandemic baseline mobility of 100%, the mobility threshold was highest in the summer (69%; interquartile range [IQR] 67%–70%), and dropped to 54% in winter 2021 (IQR 52%–55%); a mobility gap was present in Canada from July 2020 until the last week of December 2020.INTERPRETATION: Mobility strongly and consistently predicts weekly case growth, and low levels of mobility are needed to control SARS-CoV-2 through spring 2021. Mobility measures from anonymized smartphone data can be used to guide provincial and regional loosening and tightening of physical distancing measures. ER -