Dynamic Interactions of COVID-19 Incidences, Mobility, and Social Distancing Policies in Seoul: A VAR Model Approach

Background : COVID-19 incidence, mobility, and social distancing policies are interdependently linked, with the pathways and level of influence varying over time by region. Using weekly, district-specific time series data, we examined whether the effect and underlying pathways of social distancing policies on changes in COVID-19 incidence and mobility differ between commercial and non-commercial districts in Seoul. Methods: We employed the Vector Autoregression with Exogenous variables (VARX) model to analyze the interdependencies among COVID-19 incidences, mobility patterns, and social distancing policies over time from June 2020 to November 2021 across Seoul, including district-specific effects. The model incorporated vaccination coverage as an external variable to account for population-level immunity. Impulse Response Functions (IRFs) were used to interpret the results of the citywide VARX model, illustrating how changes in one variable influenced othersover time. Results: Social distancing policies had minimal direct effects on incidence rates but indirectly reduced them by decreasing mobility. Mobility observed two weeks prior demonstrated a positive correlation with current COVID-19 incidence, particularly in commercial districts, indicating that increased movement significantly contributes to transmission. On the other hand, rising COVID-19 cases led to decreased mobility, especially in non-commercial districts, likely driven by fear of infection and heightened self-restriction. Policies were more effective in reducing mobility within commercial districts, likely due to stricter enforcement and higher population density, which amplified compliance impacts. Conclusion: Reduced mobility in commercial districts following stricter policies indicates that targeted restrictions in high-traffic areas can effectively help control COVID-19 transmission in Seoul. In contrast, the more pronounced voluntary movement reductions in non-commercial areas, driven by increased incidence, suggest that enhanced regular testing could play a more significant role in disease controlin these regions. While policies reduce mobility, their slower impact on incidence rates, at least a two-week time lag, highlights the need for proactive implementation to achieve measurable decreases in transmission.