It remains one of the world's biggest mysteries: what triggered the Covid-19 pandemic? The BBC's global health correspondent Tulip Mazumdar delves into the main theories.
While politicians suspect the Wuhan Institute of Virology of having a role in starting the pandemic, most scientists think it came from the wild. Roland Pease investigates.
By Yvette Tan
By Victoria Gill
Science correspondent, BBC News
By Tara McKelvey
Supporters of former US president Donald Trump gathered near Cleveland, Ohio, on Saturday to hear him speak.
By Robin Brant
BBC News, Wuhan
Professor John Watson is a member of the World Health Organization's team investigating the origins of Covid-19.