A medical worker checks the bar code of a testing kit for COVID-19 screening at a residential area in Dongchang District of Tonghua, northeast China's Jilin Province, Jan. 25, 2021. Tonghua on Monday launched the third round of citywide nucleic acid testing. (Xinhua/Xu Chang)

A medical worker collects swab samples for COVID-19 screening at a residential area in Dongchang District of Tonghua, northeast China's Jilin Province, Jan. 25, 2021. Tonghua on Monday launched the third round of citywide nucleic acid testing. (Xinhua/Xu Chang)

Medical workers check COVID-19 screening information at a residential area in Dongchang District of Tonghua, northeast China's Jilin Province, Jan. 25, 2021. Tonghua on Monday launched the third round of citywide nucleic acid testing. (Xinhua/Xu Chang)

A medical worker collects swab samples for COVID-19 screening at a residential area in Dongchang District of Tonghua, northeast China's Jilin Province, Jan. 25, 2021. Tonghua on Monday launched the third round of citywide nucleic acid testing. (Xinhua/Xu Chang)

A medical worker knocks the door of a family to collect swab samples for COVID-19 screening at a residential area in Dongchang District of Tonghua, northeast China's Jilin Province, Jan. 25, 2021. Tonghua on Monday launched the third round of citywide nucleic acid testing. (Xinhua/Xu Chang)