The Chinese center for disease control and prevention (CDC) said China has set up three lines of defense against the possible impact of COVID-19 imported cases, including surveillance at entry points and quarantine observation.

The CDC's first line of defense is customs screening; the second line of defense is placement into isolated observation for 14 days; the third line of defense is the transfer of symptomatic patients to a hospital to be reviewed by a medical doctor.

So far, imported cases from China have largely been stuck in the first and second phases, while no one has yet to reach the third phase, suggesting that the three lines of defense are well positioned to prevent the re-emergence of COVID-19 imported cases.

Asymptomatic patients are not spreading the disease to the public as they have been in close contact with confirmed patients and were all kept in quarantine, CDC said, adding that this group will be transferred to hospital for treatment once symptoms appear.

Initial reports shows that the time of detoxification of COVID-19 is longer than that of SARS and influenza, and there is still a need to accumulate experience and data to observe the new disease, according to experts at the Department of Infectious Diseases of Peking University First Hospital.