New research on the origins of the COVID-19 outbreak puts another nail in the lab leak theory’s coffin. That theory claims the virus was either created in or studied at a laboratory in Wuhan, China, and then it either escaped accidentally or was released intentionally.

The new study shows that the virus’s path across China to Wuhan resembles that of the earlier SARS epidemic that started in 2002, in terms of time, distance, and route, they report in the journal Cell. Demonstrating its origins and route of travel essentially disputes that the virus appeared out of nowhere in Wuhan.

“The various iterations of the lab-leak theory all assume that there is something different and inexplicable about the emergence of COVID-19 compared with the emergence SARS,” says Joel Wertheim, a professor at the University of California San Diego School of Medicine, and an author of the paper, says. “There is nothing unique about how far SARS-CoV-2 had to travel to emerge in Wuhan. The SARS virus accomplished basically the same task via zoonotic emergence. Hence, there’s no need to invoke a ‘lab leak’ to explain the geography of SARS-CoV-2 emergence.”

Outbreak of COVID-19

Several earlier studies have disputed the “lab leak theory” using different methods. One 2022 paper genetically linked the earliest known human cases to a particular section of the Huanan Seafood Wholesale Market that held many wild animals and where the virus had also been detected.

Another showed that two distinct lineages of the virus existed before a different variant eventually infected humans. A third tied early versions of the virus to multiple animals in the Wuhan market.

Read More: What the Coronavirus Does to the Body

Origin of the Virus

The new study essentially pinpoints the virus’s origin to either Western China or Northern Laos several years before it infected humans. They determined that the 1,500 or so miles between those points and Wuhan was probably too far for the virus to make it within that time period by its normal method — “hitching a ride” on its primary host, the horseshoe bat.

Therefore, the virus most likely spread via a faster method, most likely via the wildlife animal trade — that same way the 2002 virus traveled. Indeed, there is nothing particularly unique about either SARS virus or about the way they traveled and eventually found their ways into humans, the researchers say.

“We see this pattern repeatedly: humans in contact with animals and the pathogens circulating among them, leading to spillovers and, at times, a devastating degree of human disease,” says Jonathan Pekar, a UCSD researcher.

Read More: Could We Be Living With COVID-19 Forever?

Tracking COVID-19 Ancestors

Some COVID-19 mysteries remain. Researchers are still trying to track down its ancestors (Wertheimer says scientists are getting closer — perhaps about two years away). And they still haven’t solved a key element in the virus’s entry into humans.

“We still haven’t nailed down the identity of the hypothetical intermediate host species that bridged the gap between bats and humans,” says Wertheim. “We have candidates. But unfortunately, we may never know.”

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Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.