The Chinese mainland has not detected any imported COVID-19 virus strains that are more powerful than the currently dominant Omicron lineages in terms of transmissibility, immune elusiveness and pathogenicity, an epidemiologist said on Thursday.

Chen Cao, a researcher at the Chinese Center for Disease Control and Prevention, said customs authorities have found 39 novel coronavirus variants so far this year on inbound travelers, all of which are Omicron subvariants.

The dominant ones are BA 5.2 and BF 7 and their subvariants, he said at a news conference in Beijing.

Speaking at the event, Wu Zunyou, chief epidemiologist at the center, said the virus has been constantly mutating globally over the past three years. In general, its transmissibility is trending stronger as it becomes less lethal, but it's becoming more elusive and more infectious, Wu added.

The new variants are posing a lesser threat to people's health as its pathogenic rate has continuously declined, from 2.33 percent in 2020 to 1.72 percent in 2021, 0.28 percent in 2022, and 0.08 in December, he said.

"The chances are slim that future mutated strains will be more infectious than today's," Wu said. "The chances of a more pathogenic variant popping up, such as one as potent as the Delta variant or the original strain, are also very small."