The coronavirus most likely emerged in bats before spreading to humans through another animal, according to a report to be released by the World Health Organization on Tuesday, offering some clues on a question that has become politically fraught amid accusations of interference from Beijing.
According to the report on the origin of the pandemic, which was obtained by The New York Times in advance of its release, a team of experts who recently visited the Chinese city of Wuhan, where the coronavirus was first detected in late 2019, also dismissed the idea that the virus might have leaked accidentally from a Chinese laboratory as “extremely unlikely.”
Officials in the United States and elsewhere have expressed concern about China’s efforts to reshape the narrative about the outbreak in Wuhan, which the authorities initially tried to conceal.
Critics have assailed the inquiry by the W.H.O. team as insufficient, saying the global health agency has been too deferential to Beijing. Chinese scientists, many of whom are affiliated with the government, helped oversee the inquiry, and the report was repeatedly delayed amid delicate negotiations with Chinese officials. For months, China sought to delay the visit of the investigators in an apparent attempt to avoid scrutiny of its early mistakes in handling the pandemic.
The Chinese government has defended its approach, saying it is fully cooperating with the W.H.O.
In the 123-page report, the scientists outlined several theories that might explain how the virus first spread to humans. The findings in the document were first reported on Monday by The Associated Press.
The report was written jointly by a team of 17 scientists from around the world and 17 Chinese scientists. The experts led a fact-finding visit to Wuhan for 27 days in January and February.
During the visit to Wuhan, Chinese officials refused to share raw data about some of the earliest possible virus cases with the W.H.O. team, frustrating some of the visiting scientists.
China’s lack of transparency as well as other concerns prompted a small group of scientists not affiliated with the World Health Organization to call this month for a new inquiry into the origin of the pandemic. They said such an inquiry should consider the possibility that the virus escaped from a laboratory in Wuhan or infected someone inside it.
The lab leak theory has been promoted by some officials in the Trump administration, including Dr. Robert Redfield, the former director of the Centers for Disease Control and Prevention, in comments to CNN last week. He offered no evidence and emphasized that it was his opinion; the theory has been widely dismissed by scientists and U.S. intelligence officials.
Matt Apuzzo contributed reporting.