Tian Ge (L) puts a swab sample tube into a bag at a building under closed-off management in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge (L) and He Yanping go to a residential area by tricycle for nucleic acid test in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

He Yanping (R) scans a resident's health code for registration for nucleic acid test at a building under closed-off management in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge (L) and He Yanping (C) check residents' information with a community staff member in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge (C) takes a swab sample from a resident for nucleic acid test at a building under closed-off management in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge (C) takes a swab sample from a resident for nucleic acid test at a building under closed-off management in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge (R) and He Yanping carry medical materials for conducting nucleic acid test in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge disinfects feet for He Yanping after conducting nucleic acid test at a building under closed-off management in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)

Tian Ge (L) and He Yanping take a swab sample from a resident for nucleic acid test at a building under closed-off management in Beicai Town of east China's Shanghai, April 26, 2022. Tian Ge and He Yanping, both general practitioners, conduct a door-to-door nucleic acid test for residents without negative results in mass testing or antigen testing in Beicai. (Xinhua/Jin Liwang)