Passengers take subway line No. 3 in Nanjing, east China's Jiangsu province, Aug. 20, 2021. Nanjing, which witnessed the country's latest resurgence of coronavirus cluster infections attributable to the Delta variant, cleared all medium- and high-risk areas for COVID-19 on Thursday. Nanjing will gradually resume the operation of public transportation now that local COVID-19 infections have been contained. (Photo: Xinhua)

Passengers take subway line No. 3 in Nanjing, east China's Jiangsu province, Aug. 20, 2021. Nanjing, which witnessed the country's latest resurgence of coronavirus cluster infections attributable to the Delta variant, cleared all medium- and high-risk areas for COVID-19 on Thursday. Nanjing will gradually resume the operation of public transportation now that local COVID-19 infections have been contained. (Photo: Xinhua)

Passengers take subway line No. 1 in Nanjing, east China's Jiangsu province, Aug. 20, 2021. Nanjing, which witnessed the country's latest resurgence of coronavirus cluster infections attributable to the Delta variant, cleared all medium- and high-risk areas for COVID-19 on Thursday. Nanjing will gradually resume the operation of public transportation now that local COVID-19 infections have been contained. (Photo: Xinhua)

Passengers take subway line No. 3 in Nanjing, east China's Jiangsu province, Aug. 20, 2021. Nanjing, which witnessed the country's latest resurgence of coronavirus cluster infections attributable to the Delta variant, cleared all medium- and high-risk areas for COVID-19 on Thursday. Nanjing will gradually resume the operation of public transportation now that local COVID-19 infections have been contained. (Photo: Xinhua)

Passengers wait for subway line No. 1 in Nanjing, east China's Jiangsu province, Aug. 20, 2021. Nanjing, which witnessed the country's latest resurgence of coronavirus cluster infections attributable to the Delta variant, cleared all medium- and high-risk areas for COVID-19 on Thursday. Nanjing will gradually resume the operation of public transportation now that local COVID-19 infections have been contained. (Photo: Xinhua)

A passenger shows health code to a staff member in subway line No. 1 in Nanjing, east China's Jiangsu province, Aug. 20, 2021. Nanjing, which witnessed the country's latest resurgence of coronavirus cluster infections attributable to the Delta variant, cleared all medium- and high-risk areas for COVID-19 on Thursday. Nanjing will gradually resume the operation of public transportation now that local COVID-19 infections have been contained. (Photo: Xinhua)