There has been no local transmission of the highly contagious Omicron subvariants XBB or BQ.1 in east China's Shanghai, a local health expert said on Monday.

Yuan Zheng'an, a member of Shanghai's COVID-19 prevention and control expert team, said the BQ.1 and XBB sublineages had only been found in a very small number of imported cases under quarantine in the city, and there had been no community infections.

XBB.1.5 has rapidly become the new dominant coronavirus subvariant in the U.S., accounting for over 40 percent of new COVID-19 cases as of last Friday, doubling from the week before, according to the U.S. Centers for Disease Control and Prevention.

XBB appears to be more immune evasive, thus more infectious. But there has been no evidence of it causing more severe illness, according to multiple media reports.  

Ling Yun, deputy director of the Shanghai Public Health Clinical Center, which is the designated hospital to receive and treat imported cases in Shanghai, said the imported cases are put under strict closed-loop management until they meet the criteria of being discharged from the hospital. He said they have found no local transmission of the said overseas strain in the city.

Read more: XBB variant: How dangerous is the newest COVID-19 strain?