The first cases identified of the Wuhan coronavirus may have occurred south of Wuhan in September, a team of scientists led by the University of Cambridge found. The South China Morning Post reported the findings on Thursday.

In a newly published study, which has not been peer-reviewed, researchers investigating the virus’s origin analyzed global viral samples and concluded that the virus must have first infected humans between September 13 and December 7.

“The virus may have mutated into its final ‘human-efficient’ form months ago, but stayed inside a bat or other animal, or even human, for several months without infecting other individuals,” University of Cambridge geneticist Peter Forster, one of the study’s researchers, said.