Even as a team of World Health Organization investigators traveled to China to research the origins of the coronavirus pandemic, critics argued that their investigation would be muzzled by a lack of cooperation from the Chinese government.
Now, the investigations team's report, obtained by ABC News ahead of its Tuesday release, is drawing renewed attention to the limits of the WHO's power.
The WHO team is facing a barrage of questions on issues of access and transparency -- even as the pandemic rages on.
Upon release of the report, WHO Director-General Tedros Adhanom Ghebreyesus noted Tuesday morning during a press conference that there's more work to be done, and that the team had "expressed the difficulties they encountered in accessing raw data."
"I do not believe that this assessment was extensive enough," Ghebreyesus said. "Further data and studies will be needed to reach more robust conclusions."
The lead investigator on the WHO-led mission, Dr. Peter Ben Embarek, emphasized the collaborative spirit in which the study was made -- though had to account for the unanswered questions still looming, acknowledging, "it's clear that there is still a lot of work to do."
The WHO is funded and run by the same group of participating member nations that sometimes come under the agency's scrutiny but -- as a governing body -- it has no multilateral regulatory or subpoena power, no skeleton key to access any country's intelligence vault. Essentially, they can only knock on the door.
"We are, for better or worse, in a situation where we're relying on countries to regulate themselves," Dr. Angela Rasmussen, a virologist and affiliate at the Georgetown Center for Global Health Science and Security and an incoming research scientist at VIDO-InterVac, told ABC News.
The WHO-led team of experts tasked with contact tracing the pandemic's origin has already been hit by criticism that the agency has not pushed hard enough for answers, though experts say they're hamstrung by their middleman role between governments and completely reliant on nations' cooperation.
The joint report from the WHO-led team and their Chinese counterparts is a culmination of the findings of an early 2021 monthlong mission to Wuhan, the site of the first major COVID-19 outbreak. It lays out an intermediary host animal as the most likely pathway for the virus' introduction and states that the lab incident theory is "extremely unlikely."
But "no firm conclusion" about the role of the Wuhan wet market in the origin of the outbreak or how the infection was introduced there "can currently be drawn," the report said. ABC News reached out to the WHO prior to the report release seeking comment but did not immediately hear back.
"You're trying to reconstruct events from a year and a half ago with incomplete sampling," Lipkin said. "That's not to cast aspersions on the team or the Chinese, because we don't ordinarily collect this sort of data … but we may never know exactly what happened."
One of the caveats to such a forensic search, experts note, is the vanishing trail of evidence and searching for clues like antibodies a year and a half after the fact raises the probability those telltale signs of infection have already dwindled.
The research lag time, paired with the report's own deadline, and goalposts which seemed to slide forward following the trip, has fomented lingering concerns. Access was a concern, experts say.
"The challenge with this report is that the WHO investigators who went [to] China did not have a real opportunity to perform a comprehensive and impartial investigation," said Dr. Krutika Kuppalli, an infectious diseases physician at the Medical University of South Carolina in Charleston.
The team's limited mandate to conduct a thorough independent investigation has been called into question numerous times by scientists and government leaders and, with the U.S. only just having recently recommitted to the WHO following former President Donald Trump's decision to pull funding, Lipkin noted that it has already made "extremely difficult" circumstances all the more complex -- particularly amid a tense geopolitical landscape and a politicized pandemic.
"We've got real concerns about the methodology and the process that went into that report, including the fact that the government in Beijing apparently helped to write it," U.S. Secretary of State Antony Blinken said in a recent CNN interview -- echoing his colleagues' calls for transparency amid criticisms that China has not been forthcoming.
White House press secretary Jen Psaki said Tuesday that while 17 U.S. government experts were still reviewing the WHO report, it “lacks crucial data, information, it lacks access, transparency."
Psaki also criticized China.
“They have not been transparent,” she said. “They have not provided underlying data. That certainly doesn’t qualify as -- as cooperation."
She said the WHO's report "doesn’t lead us to any closer of an understanding or greater knowledge than we had six to nine months ago about the origin" of the virus.
Embarek, told Science Magazine in February the team was "not naïve" about the conditions under which they and their Chinese counterparts were operating.
"Politics was always in the room with us on the other side of the table," he said.
An open letter published by a group of independent scientists in early March questioned the independence of the investigation and called for a fresh inquiry more focused on a potential lab leak -- echoed by one of its signatories Tuesday upon review of the report.
"Before almost any evidence was developed, the origin question became politicized," Dr. Steven Quay wrote in his own open letter to the WHO. "This effectively shut down any open scientific debate."
Downplaying the lab leak theory, either by deliberate bioengineering or by accident, happens to be the most decisive part of the otherwise mostly inconclusive findings.
"We've still not found the source of Ebola virus outbreaks after many years of looking," Vincent Racaniello, a Higgins professor in the Department of Microbiology and Immunology at Columbia University's College of Physicians and Surgeons, told ABC News.
For now, concerns over transparency are joined by experts' calls to think about better information sharing to better prevent the next health crisis.
"The only way that's going to happen is by focusing on improving surveillance, enhancing transparency," Lipkin said. "This is not the last pandemic. We don't even know that it's the worst, as awful as that is … so now, we need to think about public health in global terms."
ABC News' Sony Salzman, Eric M. Strauss, Connor Finnegan, Christine Theodorou and Eric Silberman contributed to this report.
Eric Silberman, MD, a resident physician in internal medicine at Northwestern Memorial Hospital, is a contributor to the ABC News Medical Unit.