More than a year after the coronavirus pandemic began, the World Health Organization released a report on Tuesday setting out theories about how the virus first spread to humans. However, it already raises more questions than answers, including from the health organ’s own head.

Written by a team of 34 Chinese scientists and international experts who led a mission in Wuhan, China, the report examines a number of politically controversial issues, including whether the virus might have accidentally emerged from a Chinese laboratory .

Some members of the expert team have raised concerns about China’s refusal to share raw data on early Covid-19 cases. In an unusual step, Dr. Tedros Adhanom Ghebreyesus, WHO Director General, raised these concerns when he spoke about the report on Tuesday. He hoped that future studies would include “a more timely and comprehensive exchange of data”.

Here’s what we know about the report.

For months, scientists, politicians and others outside of China have been advocating the theory that the virus may have emerged in China following a laboratory accident. While many experts question this theory, they have urged the WHO team to rigorously examine the possibility.

The report immediately discards the laboratory leak theory and describes it as “extremely unlikely”. The experts base their conclusion largely on discussions with scientists in Wuhan.

Dr. However, Tedros, the WHO chief, took the unexpected step of publicly casting doubt, saying the theory needed further investigation and he was ready to call in more experts.

“I do not think that this assessment was extensive enough,” he said on Tuesday at a briefing for the member states on the report. This is evident from prepared remarks published in the news media. “More data and studies are needed to reach more informed conclusions.”

The experts had said officials at the Wuhan Institute of Virology, which houses a state-of-the-art laboratory known for its research on bat coronavirus, assured them that they were not handling viruses that appeared to be closely related to the coronavirus that caused this the recent pandemic, as can be seen from the meeting notes included in the report. They also said the staff had been trained in security protocols.

The report found that a separate laboratory from the Wuhan Center for Disease Control and Prevention had moved to a new location near the Huanan Seafood Wholesale Market in Wuhan in late 2019, where many early cases of Covid-19 were occurring . The team of experts said there appeared to be no link and wrote that the lab had not reported any “incidents or incidents caused by the move” and had not conducted any coronavirus studies.

Updated

March 31, 2021, 9:45 a.m. ET

Some critics have suggested that the team appears to be taking China’s official position at face value and has not adequately investigated the laboratory officials’ claims.

Raina MacIntyre, director of the biosecurity program at the Kirby Institute at the University of New South Wales in Sydney, Australia, said the report appeared to reject the idea of ​​a laboratory leak “without strong evidence”.

“A laboratory accident is certainly a possibility,” she said.

The team of experts concluded that the coronavirus likely appeared in bats before it spread to humans via an intermediate animal. However, the team said there wasn’t enough evidence to identify the species or to pinpoint exactly where the virus was first transmitted from animals.

At the start of the pandemic, Chinese officials put forward theories suggesting that the coronavirus outbreak may have begun in the Huanan market. More than a year later, the role of animal markets in the history of the pandemic is still unclear, according to the report.

The team of experts found that many early cases had no clear link with the Huanan market, which sold sika deer, badger, bamboo rats, live crocodiles and other animals.

Of these initially confirmed cases, about 28 percent had links to the Huanan market and 23 percent were related to other markets in Wuhan, while 45 percent had no history of market exposure, according to the report.

“As such, no firm conclusion can be drawn at this time about the role of the Huanan market in causing the outbreak or how the infection was brought to the market,” the report said.

It is said that further study of farms and wildlife in China is needed and that further clues about the role of markets may emerge.

The expert team offers a long list of recommendations for additional research: more testing of wildlife and farm animals in China and Southeast Asia, more studies of the earliest cases of Covid-19, and more tracing of paths from farms to markets in Wuhan.

However, it is unclear whether China, which has repeatedly obstructed the WHO investigation, will cooperate. Chinese officials have tried to redirect attention, suggesting the virus may have emerged in the US or other countries.

Experts say the delays in the investigation have hampered the company’s ability to prevent other pandemics.

“This delay has apparently affected the investigation’s ability to reconstruct the origins of Covid-19 and find ways to reduce the risk of such events occurring again in the future,” said Michael Baker, professor of public health at the university from Otago in New Zealand.