A security guard blocks an exit as he directs people to scan a QR code to track their health status at Shanghai Hongqiao Railway Station, following new cases of the coronavirus disease (COVID-19), in Shanghai, China, November 25, 2021. Picture taken November 25, 2021. REUTERS/Aly Song

China study warns of 'colossal' COVID outbreak if it opens up

The country could face more than 630,000 COVID-19 infections a day if it dropped its zero-tolerance policies by lifting travel curbs