Medical workers collect swab samples at a nucleic acid testing site in Chengguan District of Lanzhou City, northwest China's Gansu Province, Oct. 21, 2021.Photo:Xinhua

The latest COVID-19 resurgence was triggered by a new imported source, which was diagnosed as the Delta variant, an official from the National Health Commission said at a press conference on Sunday. The official also said he anticipated the number of cases would increase in the next few days as the latest sporadic outbreaks are still at the stage of rapid development. 

Since October 17, a new round of domestic infections has been occurring in multiple places and has spread  to 11 provinces within a week. Most of the infections are related to cross-region tourism activities, according to a briefing of the NHC. 

Wu Liangyou, deputy director of the NHC disease control bureau, said that as of Saturday the total number of infections reached 133 since October 17. After tracing the sources and conducting other epidemiological investigations, 106 of them were found to be related to tourist activities involving a total of 13 tour groups or self-driving tours. 

According to the epidemiological investigations and existing virus sequencing results, the current virus genome sequence shares low homologous with the previous outbreaks in China, which suggests that the ongoing outbreaks are caused by a new imported source, Wu said. 

At present, the epidemic is at the stage of rapid development as the cases of infections that are not related to tour groups have been increasing. As the work of screening continues, the number of infections is expected to increase with the areas affected also expanding, the official noted. 

Taking into consideration the risks of COVID-19 resurgence and seasonal flu posing challenges to the anti-epidemic work in the autumn and winter seasons, the NHC urged the public to enhance immunity by taking the booster shots of COVID-19 vaccines. 

Currently, a number of high-risk groups are required to take the booster shots. Authorities demand more groups including staff working at ports, border inspection, quarantine locations and those who attend major activities or plan to go overseas for study or work, as well as groups above 60 years old who have higher risks of being infected, to be included into the groups for enhanced immunity, according to the official. 

As of Saturday, 2.24 billion doses of COVID19 vaccines have been administered across China, including 41.01 million doses received by 20.48 million people in Beijing.