Health workers collect swab samples at a COVID-19 nucleic testing site in Nandaqiao community, Chiling Road sub-district, Tianxin District of Changsha, capital of central China's Hunan Province, July 31, 2021. Local COVID-19 prevention and control authority in Changsha announced Saturday that three areas in the city have heightened their risk for COVID-19 infection from low to medium, and all-inclusive nucleic testing is now under way in these areas. (Xinhua/Chen Zeguo)