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It might take 28 consecutive days without new infection report to safely say an area is free of coronavirus, said Zhang Ying, deputy director of Tianjin Center for Disease Control and Prevention on Monday. 

As the coronavirus' incubation period is believed to be up to 14 days, two incubations are required to define an area's thorough elemination of the virus, Zhang said. 

No new confirmed cases of COVID-19 were reported Monday in 23 provincial-level regions of China, according to local health authorities. 

The development of the epidemic from the peak to the trough cannot be measured by time alone, Zhang said, adding that great efforts should be made at all levels of society.

According to Zhang, the rapid growth of the virus infection in Japan and South Korea is due to a lack of adequate understanding of the epidemic as well as self protection. 

Zhang was dubbed as "female Holmes" after detecting the contagious path of a cluster case at a shopping mall in Tinajin.

(Compiled by Shan Xin)