The Timing and Effectiveness of Implementing Mild Interventions of COVID-19 in Large Industrial Cities

Background: The outbreak of novel coronavirus disease (COVID-19) has spread around the world since it was detected in December 2019. The Chinese government executed a series of interventions to curb the pandemic. The battle against COVID-19 in Shenzhen, China is valuable because populated industrial cities are the epic centers of COVID-19 in many regions. Methods: We used synthetic control methods to compare the spread of COVID-19 between Shenzhen and its counterpart counties that didn't implement interventions for the total duration of 16 days starting from the day of the first reported case in compared locations. The hypothetical epidemic situations in Shenzhen were inferred by using time-varying reproduction numbers, assuming the interventions were delayed by 0 day to 5 days. Findings: The expected cumulative confirmed cases would be 1307, is which 4.86 times of 269 observed cumulative confirmed cases in Shenzhen on February 3, 2020, based on the data from the counterpart counties (mainly from Broward, New York, Santa Clara, Westchester and Orange) in the United States. If the interventions were delayed 5 days from the day when the interventions started, the expected cumulative confirmed cases of COVID-19 in Shenzhen on February 3, 2020 would be 676 with 95% CI (303,1959). Interpretation: Early implementation of mild interventions can subdue the epidemic of COVID-19. The later the interventions were implemented, the more severe the epidemic was in the hard-hit areas. Mild interventions are less damaging to the society but can be effective when implemented early. Funding: No funding applicable Declaration of Interests: Authors declare no competing interests.