![](http://www.ecns.cn/hd/2021/07/23/61bfecef628945fea95b09460c3d9f9f.jpg)
Medical workers take nucleic acid samples for the public at a temporary test station in Wutaishan Gymnasium, Nanjing, Jiangsu Province, July 22, 2021. The city has begun a citywide nucleic acid test since Wednesday in order to prevent the spread of the COVID-19. The sampling work is proceeding well so far. (Photo: China News Service/Yang Bo)
![](http://www.ecns.cn/hd/2021/07/23/fd2f6435789848bba36b53e1a63bfe3b.jpg)
Medical workers take nucleic acid samples for the public at a temporary test station in Wutaishan Gymnasium, Nanjing, Jiangsu Province, July 22, 2021. The city has begun a citywide nucleic acid test since Wednesday in order to prevent the spread of the COVID-19. The sampling work is proceeding well so far. (Photo: China News Service/Yang Bo)
![](http://www.ecns.cn/hd/2021/07/23/8975edb5a12f4120882f0f3774ad4594.jpg)
Medical workers take nucleic acid samples for the public at a temporary test station in Wutaishan Gymnasium, Nanjing, Jiangsu Province, July 22, 2021. The city has begun a citywide nucleic acid test since Wednesday in order to prevent the spread of the COVID-19. The sampling work is proceeding well so far. (Photo: China News Service/Yang Bo)
![](http://www.ecns.cn/hd/2021/07/23/0352a687155a497a9499bdb4702b892c.jpg)
Medical workers take nucleic acid samples for the public at a temporary test station in Wutaishan Gymnasium, Nanjing, Jiangsu Province, July 22, 2021. The city has begun a citywide nucleic acid test since Wednesday in order to prevent the spread of the COVID-19. The sampling work is proceeding well so far. (Photo: China News Service/Yang Bo)