Beijing has never fully co-operated with international investigators, impeding the search for a definitive answer. But scientists continue their quest to establish the causes of a global health crisis that killed millions of people, caused trillions of dollars of economic damage and increased fears over the risks of virus research.

Sky News host Sharri Markson is joined by author Michael Shellenberger to discuss the CIA’s recent claims that the COVID-19 pandemic was more likely originated from a lab than from nature.