A resident receives nucleic acid test at home in a residential building in Dongchang District, Tonghua City of northeast China's Jilin Province, Jan. 31, 2021. Tonghua has organized 1,030 nucleic acid test groups to conduct targeted COVID-19 screening in the high-risk zone Dongchang District since Jan. 30. (Xinhua/Xu Chang)

A medical worker prepares to conduct nucleic acid tests in a residential community in Dongchang District, Tonghua City of northeast China's Jilin Province, Jan. 31, 2021. Tonghua has organized 1,030 nucleic acid test groups to conduct targeted COVID-19 screening in the high-risk zone Dongchang District since Jan. 30. (Xinhua/Xu Chang)

Staff prepare for nucleic acid tests in a residential community in Dongchang District, Tonghua City of northeast China's Jilin Province, Jan. 31, 2021. Tonghua has organized 1,030 nucleic acid test groups to conduct targeted COVID-19 screening in the high-risk zone Dongchang District since Jan. 30. (Xinhua/Xu Chang)

A resident receives nucleic acid test at home in a residential building in Dongchang District, Tonghua City of northeast China's Jilin Province, Jan. 31, 2021. Tonghua has organized 1,030 nucleic acid test groups to conduct targeted COVID-19 screening in the high-risk zone Dongchang District since Jan. 30. (Xinhua/Xu Chang)

Staff check the information of residents for nucleic acid tests in a residential building in Dongchang District, Tonghua City of northeast China's Jilin Province, Jan. 31, 2021. Tonghua has organized 1,030 nucleic acid test groups to conduct targeted COVID-19 screening in the high-risk zone Dongchang District since Jan. 30. (Xinhua/Xu Chang)

A woman expresses gratitude to medical workers conducting nucleic acid test in a residential building in Dongchang District, Tonghua City of northeast China's Jilin Province, Jan. 31, 2021. Tonghua has organized 1,030 nucleic acid test groups to conduct targeted COVID-19 screening in the high-risk zone Dongchang District since Jan. 30. (Xinhua/Xu Chang)