BEIJING -- The XBB subvariants of Omicron are now the predominant COVID-19 strains in China, and no significant change in pathogenicity has been observed, a virology expert said Monday.

The prevalence of XBB subvariants in China surged from 0.2 percent in mid-February to 74.4 percent in late April, said Chen Cao, a research fellow at the National Institute for Viral Disease Control and Prevention under the Chinese Center for Disease Control and Prevention, at a press conference.

Of the imported COVID-19 cases, as many as 97.5 percent recorded in late April were XBB subvariants, basically consistent with the global prevalence, Chen said.

Chen said China had established a COVID-19 monitoring and warning system covering key hospitals and locations, fever clinics and urban sewage, adding that citizens should maintain good hygiene habits and respond rationally to the epidemic.