For scientists to be really convinced that the pandemic was started by a lab leak, Wertheim says there would need to be concrete evidence that the Wuhan lab had been holding a virus which matched the genetic sequence of Sars-CoV-2 partially or in full, or epidemiological data connecting some of the earliest transmission clusters to the institute.

But proving the opposite theory – that Sars-CoV-2 spilled over from the wild – is just as hard. Both the Sars and Mers outbreaks, caused by similar coronaviruses, were traced back to intermediary animal hosts – palm civets in the case of Sars, and dromedary camels in the case of Mers – which were in close contact with humans, helping the virus cross the animal-human barrier. However, while tens of thousands of animals have been tested over the past eighteen months, the search for the intermediary host of SARS-CoV-2 has been an elusive one so far.

Again, evidence has emerged that China has hindered efforts on this front. While data given to the WHO from the Chinese government suggested that only snakes, crocodiles and salamanders were being sold live in Wuhan’s wet markets, a new paper published last month revealed that in reality, 38 different species – from civet cats to raccoon dogs – were being sold between May 2017 and November 2019. “Those animals were never disclosed to the WHO in their investigation,” says Wertheim. “So there was never the opportunity to test the most relevant animals.”