A medical worker takes a swab sample from a woman at a COVID-19 nucleic acid testing site in Jiangdu District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday. (Photos: Xinhua)

A medical worker checks a resident's information before taking a swab sample at a COVID-19 nucleic acid testing site in Hanjiang District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

A medical worker takes a swab sample from a woman at a COVID-19 nucleic acid testing site in Hanjiang District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

Aerial photo taken on Aug. 9, 2021 shows a COVID-19 nucleic acid testing site in Guangling District of Yangzhou, east China's Jiangsu Province. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

A medical worker takes a swab sample from a woman at a COVID-19 nucleic acid testing site in Guangling District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

Aerial photo taken on Aug. 9, 2021 shows a COVID-19 nucleic acid testing site in Guangling District of Yangzhou, east China's Jiangsu Province. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

Residents register for COVID-19 nucleic acid tests at a testing site in Guangling District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

A medical worker disinfects a colleague at a COVID-19 nucleic acid testing site in Guangling District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.

A community service worker puts on a face shield at a COVID-19 nucleic acid testing site in Guangling District of Yangzhou, east China's Jiangsu Province, Aug. 9, 2021. The city of Yangzhou has launched its fifth round of COVID-19 mass testing on Monday.