Medical worker Cui Junyu inquires a man's health condition before his COVID-19 vaccination at the health management center in Panyu District of Guangzhou City, south China's Guangdong Province, Jan. 6, 2021. (Xinhua/Xu Hongyi)

Medical worker Zeng Jingyi shows her COVID-19 vaccine tracing information on a phone app developed by the provincial center for disease control and prevention, at the health management center in Panyu District of Guangzhou City, south China's Guangdong Province, Jan. 6, 2021. (Xinhua/Xu Hongyi)

A medical worker injects COVID-19 vaccine to a man at the health management center in Panyu District of Guangzhou City, south China's Guangdong Province, Jan. 6, 2021. (Xinhua/Xu Hongyi)

A medical worker shows the COVID-19 vaccine developed by Beijing Biological Products Institute Co., Ltd. at the health management center in Panyu District of Guangzhou City, south China's Guangdong Province, Jan. 6, 2021. (Xinhua/Xu Hongyi)