Medical workers collect swab samples from residents at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Ju Huanzong)

A medical worker collects a swab sample from a child at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Peng Ziyang)

A medical worker collects a swab sample from a resident at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Ju Huanzong)

A medical worker collects a swab sample from a child at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Ju Huanzong)

A medical worker collects a swab sample from a child at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Ju Huanzong)

A medical worker collects a swab sample from a child at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Peng Ziyang)

A staff member guides residents at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Peng Ziyang)

A medical worker collects a swab sample from a resident at a COVID-19 testing site in Daxing District of Beijing, capital of China, Jan. 26, 2021. Beijing started a second round of mass nucleic acid testing in Daxing District on Tuesday, in an effort to contain the latest COVID-19 resurgence. (Xinhua/Peng Ziyang)