Residents take nucleic acid test in Changchun

A medical worker takes a swab sample from a resident for nucleic acid test at a COVID-19 testing site in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Photo by Zhang Yang/Xinhua)

A medical worker takes a swab sample from a resident for nucleic acid test at a COVID-19 testing site in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Xinhua/Zhang Jian)

A volunteer helps a resident register for nucleic acid test in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Photo by Zhang Yang/Xinhua)

A medical worker takes a swab sample from a resident for nucleic acid test at a COVID-19 testing site in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Xinhua/Zhang Jian)

A medical worker takes a swab sample from a resident for nucleic acid test at a COVID-19 testing site in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Photo by Zhang Yang/Xinhua)

Medical workers take swab samples from residents for nucleic acid test at a COVID-19 testing site in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Xinhua/Zhang Jian)

A volunteer uses a loudspeaker to remind residents to take nucleic acid test in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Photo by Zhang Yang/Xinhua)

A resident scans QR code to register for nucleic acid test at a COVID-19 testing site in Changchun, northeast China's Jilin Province, March 21, 2022. Changchun rolled out a new round of mass nucleic acid test on Sunday as a measure to combat the latest COVID-19 resurgence. (Xinhua/Zhang Jian)