Fig. 4

Actual and threshold of spatial spillover risk (A The newly reported confirmed cases and asymptomatic cases of each city were illustrated in light blue and dark blue columns. The threshold of spillover risk of each city was shown in pink lines with quartile 25 and quartile 75 in pink shades. B The solid line represents the spillover risk, and the positive and inverted triangles represent the duration start and end, respectively. The actual spillover rates of the study regions are distinguished by different colors: Shanghai (blue), Shenzhen (orange), Nanjing (green), and Suzhou (red))