Medical workers prepare to carry out nucleic acid tests at a nucleic acid testing site in Qingpu District of east China's Shanghai, March 14, 2022. Medical workers from the Xianghuaqiao community medical service center in Qingpu District of Shanghai joined the battle against the recent COVID-19 resurgence. They have collected more than 56,000 samples for nucleic acid testing since the latest resurgence in March. (Photo by Shen Yiqing/Xinhua)

Medical workers prepare to carry out nucleic acid tests at a nucleic acid testing site in Qingpu District of east China's Shanghai, March 14, 2022. Medical workers from the Xianghuaqiao community medical service center in Qingpu District of Shanghai joined the battle against the recent COVID-19 resurgence. They have collected more than 56,000 samples for nucleic acid testing since the latest resurgence in March. (Photo by Shen Yiqing/Xinhua)

Medical workers prepare to carry out nucleic acid tests at a university in Qingpu District of east China's Shanghai, March 14, 2022. Medical workers from the Xianghuaqiao community medical service center in Qingpu District of Shanghai joined the battle against the recent COVID-19 resurgence. They have collected more than 56,000 samples for nucleic acid testing since the latest resurgence in March. (Photo by Shen Yiqing/Xinhua)

A medical worker takes a swab sample from a student for nucleic acid test at a university in Qingpu District of east China's Shanghai, March 14, 2022. Medical workers from the Xianghuaqiao community medical service center in Qingpu District of Shanghai joined the battle against the recent COVID-19 resurgence. They have collected more than 56,000 samples for nucleic acid testing since the latest resurgence in March. (Photo by Shen Yiqing/Xinhua)

A medical worker takes a swab sample from a student for nucleic acid test at a university in Qingpu District of east China's Shanghai, March 14, 2022. Medical workers from the Xianghuaqiao community medical service center in Qingpu District of Shanghai joined the battle against the recent COVID-19 resurgence. They have collected more than 56,000 samples for nucleic acid testing since the latest resurgence in March. (Photo by Shen Yiqing/Xinhua)