CNN  — 

The novel coronavirus that causes Covid-19 probably spread to people through an animal, and probably started spreading among humans no more than a month or two before it was noticed in December of 2019, according a new 120-page report from the World Health Organization.

But the search for the origin of the virus is ongoing.

“As far as WHO is concerned, all hypotheses remain on the table,” WHO Director-General Tedros Adhanom Ghebreyesus said in a statement Tuesday. “This report is a very important beginning, but it is not the end. We have not yet found the source of the virus, and we must continue to follow the science and leave no stone unturned as we do.”

The report, released Tuesday, lists four commonly discussed scenarios for the virus’ introduction to humans, including two it says are unlikely.

It says a scenario where the virus spread via an intermediate animal host, possibly a wild animal captured and then raised on a farm, is “very likely.” But the investigation has not found what other animal was infected by a bat – considered the most likely original source of the virus – and then may have transmitted it to a human. “The possible intermediate host of SARS-CoV-2 remains elusive,” the report reads.

Next likely is direct transmission from one of the animals known to carry a similar coronavirus, such as a bat or a pangolin.

The report says introduction through cold food products is considered a “possible pathway” and introduction through a laboratory incident was considered to be “an extremely unlikely pathway.”

The governments of the United States Australia, Canada, Czechia, Denmark, Estonia, Israel, Japan, Latvia, Lithuania, Norway, the Republic of Korea, Slovenia, and the United Kingdom jointly expressed concern about the World Health Organization (WHO) study into the origins of Covid-19 in China and called for independent and fully transparent evaluations with access to all relevant data in the future.

“We join in expressing shared concerns regarding the recent WHO-convened study in China, while at the same time reinforcing the importance of working together toward the development and use of a swift, effective, transparent, science-based, and independent process for international evaluations of such outbreaks of unknown origin in the future,” Tuesday’s joint statement said.

WHO scientists say they didn’t do ‘forensic examination’ of lab leak theory

The WHO report was written by a joint international team made up of 17 Chinese experts plus 17 experts from other countries, WHO, the Global Outbreak Alert and Response Network (GOARN) and the World Organization for Animal Health (OIE). The United Nations Food and Agriculture Organization of the United Nations (FAO) participated as an observer.

The original mission of WHO scientists was to study the animal origin of the novel coronavirus, which is why the new report does not provide the same depth of detail examining a lab leak theory, Peter Ben Embarek, a member of the WHO investigation team, said during a news briefing on Tuesday.

“The team was put together to do studies into the zoonotic origin of this virus,” Ben Embarek said, adding that this is the first time the scientists have been able to openly discuss the lab leak possibility.

“Now we have a process to discuss it – we have put it in our report,” Ben Embarek said. “Since this was not the key or main focus of the studies, it did not receive the same depth of attention and work as the other hypotheses.”

Still, the theory continues to draw attention. Former US Centers for Disease Control and Prevention Director Dr. Robert Redfield previously told CNN’s Dr. Sanjay Gupta in the documentary, “