Background In December 2019, an outbreak of COVID-19 epidemic occurred in Wuhan, China and infection spread rapidly around the world. To limit the rapid spread locally and nationwide, the Chinese government locked down Wuhan city on January 23 and began implementing nationwide intensive community screening on February 16.

In December 2019, an outbreak of COVID-19 epidemic occurred in Wuhan, China and this infection has spread rapidly into more than 109 countries around the world.To limit the rapid spread in community and nationwide, Wuhan city lockdown and nationwide intensive community screening were employed by Chinese government.To assess the effectiveness of city lockdown and intensive community screening, we built a modified SIR model by introducing an α value into the classic SIR model. The α value represents the proportion of the infected that is not effectively isolated from the susceptible at a given time point. The α value of China excluding Hubei province was largely reduced by Wuhan city lockdown. Although the α value of Wuhan city dropped a little with city lockdown, but dropped rapidly with intensive community screening. With the decrease of α value, the epidemic in China would be end at the beginning of June 2020. With current epidemiological data, the infection cases in South Korea and Italy are predicted to increase exponentially in the next days, if stringent mitigation measures were not adopted.

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