A medical worker works at the polymerase chain reaction (PCR) laboratory in Beijing Puren Hospital in Beijing, capital of China, June 23, 2020. The PCR lab was put into use on June 15 to conduct nucleic acid testing for COVID-19. (Xinhua/Zhang Yuwei)

Medical worker Yang Huijuan walks out of the polymerase chain reaction (PCR) laboratory in Beijing Puren Hospital in Beijing, capital of China, June 23, 2020. The PCR lab was put into use on June 15 to conduct nucleic acid testing for COVID-19. (Xinhua/Zhang Yuwei)

A medical worker works at the polymerase chain reaction (PCR) laboratory in Beijing Puren Hospital in Beijing, capital of China, June 23, 2020. The PCR lab was put into use on June 15 to conduct nucleic acid testing for COVID-19. (Xinhua/Zhang Yuwei)

A medical worker operates an instrument to conduct nucleic acid extraction at the polymerase chain reaction (PCR) laboratory in Beijing Puren Hospital in Beijing, capital of China, June 23, 2020. The PCR lab was put into use on June 15 to conduct nucleic acid testing for COVID-19. (Xinhua/Zhang Yuwei)