  In order to investigate the effectiveness of lockdown and social distancing
restrictions, which have been widely carried out as policy choice to curb the
ongoing COVID-19 pandemic around the world, we formulate and discuss a staged
and weighed networked system based on a classical SEAIR epidemiological model.
Five stages have been taken into consideration according to four-tier response
to Public Health Crisis, which comes from the National Contingency Plan in
China. Staggered basic reproduction number has been derived and we evaluate the
effectiveness of lockdown and social distancing policies under different
scenarios among 19 cities/regions in mainland China. Further, we estimate the
infection risk associated with the sequential release based on population
mobility between cities and the intensity of some non-pharmaceutical
interventions. Our results reveal that Level I public health emergency response
is necessary for high-risk cities, which can flatten the COVID-19 curve
effectively and quickly. Moreover, properly designed staggered-release policies
are extremely significant for the prevention and control of COVID-19,
furthermore, beneficial to economic activities and social stability and
development.
