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.

Langley joins the FBI and Energy Department in agreeing that a lab leak is the most likely source of the pandemic.

The nuanced finding suggests the agency believes the totality of evidence makes a lab origin more likely than a natural origin.