A health worker collects nucleic acid sample from a resident for COVID-19 test at a community in Jiangning District of Nanjing, capital of east China's Jiangsu Province, July 24, 2021. A second round of COVID-19 nucleic acid test was launched Saturday in Jiangning District of Nanjing. The eastern Chinese city on Friday reported 12 new locally transmitted COVID-19 cases and four asymptomatic ones, local health authorities said on Saturday. (Xinhua/Ji Chunpeng)