According to a report in AFP, while experts believe that the disease originated from bats, and could have been transmitted to humans via another mammal, WHO foreign expert Peter Ben Embarek said putting animals in the picture is a "work in progress".

The absense of bats in Wuhan was also a factor to be considered when talking about direct transmission from these animals.

Leak from lab

Other than that, Ben Embared also invalidated the theory that the pandemic was caused by a lead from a virology lab in Wuhan.

"The laboratory incident hypothesis is extremely unlikely," he said, explaining that it "is not in the hypotheses that we will suggest for future studies."

Meanwhile, Liang Wannian, head of the China side of the joint mission, said animal transmission remained the most likely route, but said that "the reservoir hosts remain to be identified."