A medical worker collects a swab sample from a resident at a coronavirus testing site in Tiexi District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Pan Yulong)

A medical worker collects a swab sample from a resident at a coronavirus testing site in Tiexi District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Pan Yulong)

Aerial photo shows residents waiting in line for nucleic acid tests at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Yang Qing)

Medical workers prepare for nucleic acid sampling at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Yang Qing)

A medical worker collects a swab sample from a resident at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Cai Xiangxin)

A medical worker collects a swab sample from a resident at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Yang Qing)

Medical workers collect swab samples from residents at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Cai Xiangxin)

Residents wait in line for nucleic acid tests at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Yang Qing)

Residents wait in line for nucleic acid tests at a coronavirus testing site in Tiexi District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Pan Yulong)

Medical workers prepare for nucleic acid sampling at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Yang Qing)

Residents wait in line for nucleic acid tests at a coronavirus testing site in Huanggu District of Shenyang, northeast China's Liaoning Province, Jan. 4, 2021. Shenyang is conducting a second round of nucleic acid tests for all residents in Texi, Huanggu and Yuhong districts, starting Monday. (Xinhua/Yang Qing)