Fig. 2

The panel at the top corresponds to the epidemic in Xi’an, and the panel at the bottom corresponds to the epidemic in Shanghai. Bars in light gray and in dark gray represent the number of daily reported cases in control zones and in society, respectively. The black curve is the effective reproduction number \({R}_{t}^{{s}_{1}}\) through time \(t\) in society, which is calculated by assuming that there are no internal infections in the control zone, i.e., the scenario (a) in Fig. 1. The size of \({R}_{t}^{{s}_{1}}\) is measured by the right y-axis. When \({R}_{t}^{{s}_{1}}\) is above the threshold value of one, i.e., the horizontal dashed line in red, the epidemic shows an upward trend; otherwise, it is under control