A medical worker takes a swab sample from a kid for nucleic acid test at a testing site in Nanjing, capital of east China's Jiangsu Province, July 29, 2021. Nanjing, a mega-city with a population of more than 9.3 million in eastern China, launched the third round of all-inclusive nucleic acid testing campaign on Wednesday, according to the municipal COVID-19 prevention and control headquarters. The citywide testing covers all residents, including those who are paying a short visit to the city. (Xinhua/Ji Chunpeng)