A worker performs a quality check in the packaging facility of Chinese vaccine maker Sinovac Biotech, developing an experimental coronavirus disease (COVID-19) vaccine, during a government-organized media tour in Beijing, China, September 24, 2020. China's Sinovac Biotech expects to begin analysing final-stage human trial data on its coronavirus vaccine candidate this year to decide whether it is effective enough to seek regulatory approval before trial completion. REUTERS/Thomas Peter

A man works in a laboratory of Chinese vaccine maker Sinovac Biotech, developing an experimental coronavirus disease (COVID-19) vaccine, during a government-organized media tour in Beijing, China, September 24, 2020. Sinovac can start assessing CoronaVac's ability to protect people as soon as researchers observe at least 61 trial subjects get sick from the disease. REUTERS/Thomas Peter

A man works in a laboratory of Chinese vaccine maker Sinovac Biotech, developing an experimental coronavirus disease (COVID-19) vaccine, during a government-organized media tour in Beijing, China, September 24, 2020. China's Sinovac Biotech hopes to supply its experimental coronavirus vaccine to more South American countries by outsourcing some manufacturing procedures to a partner in Brazil. REUTERS/Thomas Peter

A worker performs a quality check in the packaging facility of Chinese vaccine maker Sinovac Biotech, developing an experimental coronavirus disease (COVID-19) vaccine, during a government-organized media tour in Beijing, China, September 24, 2020. China included Sinovac's vaccine candidate CoronaVac in its emergency use programme launched in July, but late-stage trials overseas have not been completed, arousing safety concerns among experts. REUTERS/Thomas Peter

A man works in the packaging facility of Chinese vaccine maker Sinovac Biotech, developing an experimental coronavirus disease (COVID-19) vaccine, during a government-organized media tour in Beijing, China, September 24, 2020. REUTERS/Thomas Peter