The lack of data potentially complicating efforts to understand how the outbreak began over a year ago, after it was first detected in China's Wuhan.
The team had requested raw patient data on the 174 cases of COVID-19 that China had identified from the early phase of the outbreak in Wuhan in December 2019, as well as other cases.
However, they were only provided with a summary, said Dominic Dwyer, an Australian infectious diseases expert who is a member of the team.
Pictured: Dominic Dwyer, a member of the World Health Organization (WHO) team tasked with investigating the origins of the coronavirus disease (COVID-19), responds to journalists' questions, from a balcony at a hotel in Wuhan, China on January 29, 2021
Such raw data is known as 'line listings', he said, and would typically be anonymised but contain details such as what questions were asked of individual patients, their responses and how their responses were analysed.
'That's standard practice for an outbreak investigation,' he told Reuters on Saturday via video call from Sydney, where he is currently undergoing quarantine.
He said that gaining access to the raw data was especially important since only half of the 174 cases had exposure to the Huanan market, the now-shuttered wholesale seafood centre in Wuhan where the virus was initially detected.
'That's why we've persisted to ask for that,' he said. 'Why that doesn't happen, I couldn't comment,' he said.
'Whether it's political or time or it's difficult ... But whether there are any other reasons why the data isn't available, I don't know. One would only speculate.'
While the Chinese authorities provided a lot of material, he said the issue of access to the raw patient data would be mentioned in the team's final report.
'The WHO people certainly felt that they had received much much more data than they had ever received in the previous year. So that in itself is an advance.'
A summary of the team's findings could be released as early as next week, the WHO said on Friday.
The WHO-led probe had been plagued by delay, concern over access and bickering between Beijing and Washington, which accused China of hiding the extent of the initial outbreak and criticised the terms of the visit, under which Chinese experts conducted the first phase of research.
The team, which arrived in China in January and spent four weeks looking into the origins of the COVID-19 outbreak, was limited to visits organised by their Chinese hosts and prevented from contact with community members, due to health restrictions. The first two weeks were spent in hotel quarantine.
The head of WHO on Friday insisted that the theory Covid-19 emerged in a laboratory in Wuhan has not been dismissed following a controversial fact-finding mission to China. Pictured: WHO director-general Tedros Adhanom Ghebreyesus
There have been fears the mission would become part of Chinese white-washing exercise with potentially embarrassing or incriminating evidence hidden from researchers. Pictured: President Xi Jinping, addresses a Chinese Lunar New Year reception at the Great Hall of the People in Beijing, China, February 10
China's refusal to hand over raw data on the early COVID-19 cases was reported earlier by the Wall Street Journal on Friday.
The WHO did not reply to a request from Reuters for comment. The Chinese foreign ministry did not immediately reply to a request for comment but Beijing has previously defended its transparency in handling the outbreak and its cooperation with the WHO mission.
Dwyer said the work within the WHO team was harmonious but that there were 'arguments' at times with their Chinese counterparts over the interpretation and significance of the data, which he described as 'natural' in such probes.
'We might be having a talk about cold chain and they might be more firm about what the data shows than what we might have been, but that's natural.
'Whether there's political pressure to have different opinions, I don't know. There may well be, but it's hard to know.'
Cold chain refers to the transport and trade of frozen food.
Beijing has sought to cast doubt on the notion that the coronavirus originated in China, pointing to imported frozen food as a conduit.
Pictured: People watch a traditional dragon dance performance during the second day of Spring Festival in Han Kou Li on February 13 in Wuhan - where the virus was first detected
On Tuesday, Peter Ben Embarek, who led the WHO delegation, told a news conference that transmission of the virus via frozen food is a possibility, but pointed to market vendors selling frozen animal products including farmed wild animals as a potential pathway that warrants further study.
Embarek also said that the team was not looking further into the theory that the virus escaped from a lab, which it considered highly unlikely.
The previous U.S. administration of President Donald Trump had said it suspected the virus may have escaped from a Wuhan lab, which Beijing strongly denies.
'It was an unanimous feeling,' Dwyer said. 'It wasn't a political sop whatsoever.'
WHO backtracks on Covid Wuhan lab: Theory that virus emerged in laboratory has NOT been dismissed, health chief insists - as it emerges China WON'T hand over raw data on early infections
By Faith Ridler For Mailonline, 12 February 2021
The investigation to Wuhan, where the first cases were detected, failed to identify the source of the virus but appeared to disregard the theory that it leaked from a virology laboratory in the city.
However, WHO director-general Tedros Adhanom Ghebreyesus today said that following the 'very important scientific exercise ... all hypotheses remain open and require further analysis and studies.'
It comes after Peter Embarek, the leader of the WHO team, this week concluded it was 'extremely unlikely' that the virus emerged from the Wuhan Institute of Virology.
Shi Zhengli works with other researchers in a lab at the Wuhan Institute of Virology in Wuhan in central China's Hubei province in February 2017
Speaking from Geneva today, Dr Tedros said: 'Some questions have been raised as to whether some hypotheses have been discarded.
'Having spoken with some members of the team, I wish to confirm that all hypotheses remain open and require further analysis and studies.
'Some of that work may lie outside the remit and scope of this mission. We have always said that this mission would not find all the answers, but it has added important information that takes us closer to understanding the origins of the virus.
'The mission achieved a better understanding of the early days of the pandemic, and identified areas for further analysis and research. And we will continue working to get the information we need to answer the questions that still need to be answered.'
Did coronavirus originate in Chinese government laboratory?
The Wuhan Institute of Virology has been collecting numerous coronaviruses from bats ever since the SARS outbreak in 2002.
They have also published papers describing how these bat viruses have interacted with human cells.
US Embassy staff visited the lab in 2018 and 'had grave safety concerns' over the protocols which were being observed at the facility.
The lab is just eight miles from the Huanan wet market which is where the first cluster of infections erupted in Wuhan.
The market is just a few hundred yards from another lab called the Wuhan Centers for Disease Prevention and Control (WHCDC).
The WHCDC kept disease-ridden animals in its labs, including some 605 bats.
Those who support the theory argue that Covid-19 could have leaked from either or both of these facilities and spread to the wet market.
Most argue that this would have been a virus they were studying rather than one which was engineered.
Last year a bombshell paper from the Beijing-sponsored South China University of Technology recounted how bats once attacked a researcher at the WHCDC and 'blood of bat was on his skin.'
The report says: 'Genome sequences from patients were 96% or 89% identical to the Bat CoV ZC45 coronavirus originally found in Rhinolophus affinis (intermediate horseshoe bat).'
It describes how the only native bats are found around 600 miles away from the Wuhan seafood market and that the probability of bats flying from Yunnan and Zhejiang provinces was minimal.
In addition there is little to suggest the local populace eat the bats as evidenced by testimonies of 31 residents and 28 visitors.
Instead the authors point to research being carried out within 300 yards at the WHCDC.
One of the researchers at the WHCDC described quarantining himself for two weeks after a bat's blood got on his skin, according to the report. That same man also quarantined himself after a bat urinated on him.
And he also mentions discovering a live tick from a bat - parasites known for their ability to pass infections through a host animal's blood.
'The WHCDC was also adjacent to the Union Hospital (Figure 1, bottom) where the first group of doctors were infected during this epidemic.' The report says.
'It is plausible that the virus leaked around and some of them contaminated the initial patients in this epidemic, though solid proofs are needed in future study.'
It comes as it emerged China refused to provide WHO investigators with 'raw, personalised data' on early coronavirus cases that could help them figure out how and when the virus first began to spread.
Authorities reportedly refused requests to provide this data on 174 cases of Covid-19 that were identified from the early outbreak in December 2019, the Wall Street Journal reported.
Dominic Dwyer, an Australian microbiologist on the WHO team, said: 'They showed us a couple of examples, but that's not the same as doing all of them, which is standard epidemiological investigation.
'So then, you know, the interpretation of that data becomes more limited from our point of view, although the other side might see it as being quite good.'
It was said that China provided their own analysis of data on these cases, but would not provide the raw data which would have allowed WHO experts to carry out their own studies.
Earlier, Mr Embarek said it was 'extremely unlikely' the virus emerged from a lab in Wuhan, adding: 'It is not in the hypotheses that we will suggest for future studies.'
The findings amount to an almost full backing of Beijing's explanations for the source of the pandemic and will be a PR coup for the ruling communist party, which has repeatedly tried to pin the blame outside its borders.
It will also give ammunition to WHO's critics, who feared the investigation would be used to give legitimacy to a Chinese white-washing exercise with possibly embarrassing or incriminating evidence hidden from investigators.
It is hardly the first time that the WHO has come under fire for uncritically parroting information from Beijing - ex-President Trump made the same allegations last year before pulling US funding, a move that President Biden has now pledged to reverse.
Dr Tedros has also come in for heavy criticism for his praise of China - describing its 'commitment to transparency' as 'beyond words' during the early stages of the outbreak, despite strong doubts about data coming from Beijing and a past history of covering up disease outbreaks.
It was also revealed that Dr Tedros received support from Beijing while in the running to become WHO chief, and that China has often donated large sums of money to governments or organisations that he has been a part of.
During his press conference, Dr Embarek also backed assertions from Beijing that there is no evidence of transmission 'in Wuhan or elsewhere' in China before December 2019 - despite multiple studies suggesting the virus was circulating globally months earlier than that.
Outlining the findings of his team's month-long fact-finding mission, Dr Embarek said the team had failed to establish where the virus came from or how it first jumped into humans. Instead, he said the team had come up with four theories about its origins.
He said the most likely explanation is that the virus passed from its original host animal into an intermediary animal that comes into close contact with humans, before making the leap into people.
Intermediary animals could include frozen or chilled animal products sold at markets in Wuhan, including those imported from overseas, he said, outlining his second theory.
The next most-likely theory is that the virus jumped directly from its original host into humans, Dr Embarek said, putting forward bats as a likely source.
But, he said, humans and bats do not come into close contact in Wuhan and swabs of bats and various other animal species in China - including wild animals, pets, and farm animals - has failed to find the original source.
Dr Embarek called for more research to be carried out into all three of these theories, and said teams should be looking outside as well as inside of China's borders.
Dr Tedros today said he hoped a summary report from the mission would be published next week, with the full final report to follow in the coming weeks.
Multiple countries have uncovered evidence that the virus was circulating months earlier than originally thought. While Beijing has tried to insist this proves the virus originated elsewhere, most scientists still think China was the origin - raising the prospect that communist officials simply hid evidence of the early spread
Chinese scientists and officials have been keen to point the finger of blame outside their own borders - variously suggesting that the virus could have originated in Bangladesh, the US, Greece, Australia, India, Italy, Czech Republic, Russia or Serbia
China's official timeline vs new evidence
Dec 8, 2019 - Earliest date that China has acknowledged an infection
Dec 31 - China first reported 'pneumonia of unknown cause' to the World Health Organisation
Jan 1, 2020 - Wuhan seafood market closed for disinfection
Jan 11 - China reported its first death
Jan 23 - Wuhan locked down
Jan 31 - WHO declared 'outbreak of international concern' as China admitted having thousands of cases
Feb 23 - Italy reports cluster of cases in first major outbreak in the West
Sep 2019- Blood samples are taken in a lung cancer screening trial in Italy which later test positive for coronavirus
Oct-Dec - Rise in 'flu and pneumonia' cases in northern Italy which could be linked to coronavirus
Nov - Sewage samples taken in Florianópolis, Brazil, suggest virus was present
Nov 10 - Milanese woman has a skin biopsy, producing a sample which later shows signs of the virus
Nov 17 - Leaked documents suggest case detected in China on this date
Dec 1 - Chinese researchers report an infection on this date in a peer-reviewed study, but it has not been acknowledged by Beijing
Dec 18 - Sewage samples taken in Milan and Turin suggest virus was circulating in the cities
Jan 2020 - Sewage samples from Barcelona suggest virus was in the city