Evaluating Apple Inc. mobility trend data related to the COVID-19 outbreak in Japan (Preprint)
BACKGROUND In Japan, as a countermeasure against the COVID-19 outbreak, voluntary restrictions against going out (VRG) from a residence were announced from the end of March by national and local governments in preference to lockdowns like those instituted in European and North American countries. OBJECTIVE We examined some associations among going out information provided by Apple Inc. and estimated an effective reproduction number R(t). METHODS We regressed R(t) on a polynomial function of daily Apple Inc. data. From estimation using the whole period, the sub-periods delimited by March 10 were analyzed. RESULTS Estimation results indicate R(t) as 1.72 if VRG ceases and mobility reverts to a normal level. However, the critical level of R(t)<1 was achieved at a 89.3% of the normal level of mobility. CONCLUSIONS Results indicate that a 10% reduction from the normal number of trips will be necessary until herd immunity is achieved. Complete cessation of VRG might not be necessary to avoid re-emergence of the outbreak.