From This World, BBC Two (UK). On the 23rd of January last year Chinese authorities announced they were locking down the city of Wuhan, home to some eleven million people. The Chinese government was desperate to contain an outbreak of a new virus that would soon be labelled COVID-19. What they didn't reveal was that the virus had already been circulating for at least seven weeks while Chinese officials tried to stop the news of it getting out. Four Corners brings you an investigation into what the Chinese government knew about the virus and compelling evidence of a determined campaign to keep it under wraps.