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. (Photos: Xinhua)

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.

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.

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.

A resident registers for nucleic acid tests 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.

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.

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.

A volenteer 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.

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.

Residents wait in line for nucleic acid tests 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.

Residents wait in line for nucleic acid tests 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.

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.

Residents wait in line for nucleic acid tests 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.