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.

Ex-CNN editor Chris Cilizza conceded on Monday that he "screwed up" in his assessment of the lab leak theory, suggesting that President Trump was likely right about COVID's origins.

After years of speculation, the CIA has weighed in yet again: A lab leak is now considered the likely origin of the COVID pandemic. However, the agency admits it has "low confidence" in its conclusion and says both a natural origin and a research-related incident are still possible.