BEIJING, Oct. 24 (Xinhua) -- Epidemiological investigation and viral genome sequencing results in hand have indicated that this new round of COVID-19 infections in China was caused by viruses transmitted from abroad, according to the National Health Commission (NHC).

A medical worker collects a swab sample at a nucleic acid testing site in Ejina Banner of Alxa League, north China's Inner Mongolia Autonomous Region, Oct 22, 2021. (Photo: Xinhua)

The Delta variant is behind the fresh COVID-19 cases, Wu Liangyou, an official with the NHC, said at a press conference, adding that efforts are still being made to trace the origins.