"The novel coronavirus will remain in the body for quite a long time," said Wang Guiqiang of the Department of Infection, Peking University First Hospital, on Tuesday at a daily press conference.

Compared to the viruses that cause seasonal influenza and severe acute respiratory syndrome (SARS), it will take a longer time to get the novel coronavirus out of the human body once infected, he added.

That may partly explain why some patients again test positive for the virus after recovery. Experts noted this situation doesn't mean these people get a second infection. It was either because test samples were not collected properly or the patients were still in a long course of the disease with a very low viral load level.

Besides, COVID-19 is much more contagious but less deadly than SARS, less contagious but more deadly than common flu, Wang added.

The novel virus belongs to the same coronavirus family as SARS. But it has mutated, including its genetic sequence and molecular structure.

According to Zhi Xiuyi, director of Lung Cancer Diagnosis and Treatment Center of Capital Medical University, though current data shows that COVID-19 is more transmissible than SARS, its fatality rate has been lower.

More than 420,000 people have been infected in over 150 countries, with the death toll climbing to at least 18,915, according to the Johns Hopkins University Center for Systems Science and Engineering.

"The severity of the infection is expected to decrease over time as the virus adapts to humans. It would then not be surprising if the virus caused flu-like illness like other human coronaviruses," said Benjamin Joh, a professor at the School of Public Health at Hong Kong University.