Experts studying the origins of the coronavirus for the World Health Organization warned on Wednesday that the inquiry had “stalled” and that further delays could make it impossible to recover crucial evidence about the beginning of the pandemic.
“The window is rapidly closing on the biological feasibility of conducting the critical trace-back of people and animals inside and outside China,” the experts wrote in an editorial in the journal Nature. Several studies of blood samples and wildlife farms in China were urgently needed to understand how Covid-19 emerged, they said.
Amid a rancorous debate about whether a laboratory incident could have started the pandemic, the editorial amounted to a defense of the team’s work and an appeal for follow-up studies. A separate report by American intelligence agencies into the pandemic’s origins was delivered to President Biden on Tuesday, but did not offer any new answers about whether the virus emerged from a lab or in a natural spillover from animals to humans.
The international expert team, sent to Wuhan, China, in January as part of a joint inquiry by the World Health Organization and China, has faced criticism for publishing a report in March that said a leak of the coronavirus from a lab, while possible, was “extremely unlikely.”
Immediately after the report’s release, Dr. Tedros Adhanom Ghebreyesus, the W.H.O.’s director-general, said that the study had not adequately assessed the possibility of a lab leak.
Virologists have leaned toward the theory that infected animals spread the virus to people. In the editorial published on Wednesday, the expert team reiterated calls to test the blood of workers on wildlife farms that supplied animals to Wuhan markets, to see if they carried antibodies indicating past coronavirus infections. The team also recommended screening more farmed wildlife or livestock that could have been infected. (The editorial also notes, somewhat pessimistically, that many Chinese wildlife farms have been closed and their animals killed since the pandemic emerged, making evidence of early spillover from animals to humans hard to come by.)
The team pointed to a recent report showing that markets in Wuhan had sold live animals susceptible to the virus, including palm civets and raccoon dogs, in the two years before the pandemic began, and argued that the weight of evidence behind a natural spillover was greater than that for a lab leak.
Marion Koopmans, a Dutch virologist and co-author of the editorial, described it in an interview as a “cry for urgency.”
“We were getting a little concerned that there really is virtually no debate about the bulk of the recommendations that are not related to the lab hypothesis, and of course there’s a lot of discussion of the lab story, particularly coming from the U.S.,” she said. “Our concern is that because of that emphasis, the rest doesn’t get any more attention.”
To identify the first cases of the virus, Dr. Koopmans said, scientists also needed to examine blood specimens from late 2019 before they are thrown away. The expert team received assurances on its visit to Wuhan that blood banks there would keep samples beyond the usual two-year period, she said, but has still not received access to them.
The Chinese government has stopped cooperating with investigations by the W.H.O., making it difficult to assess any theories about the virus’s origins.
Michael Ryan, a W.H.O. official, criticized China at a news conference on Wednesday for pushing unproven ideas suggesting that the coronavirus escaped from an American military lab.
“It is slightly contradictory if colleagues in China are saying that the lab leak hypothesis is unfounded in the context of China, but we now need to go and do laboratory investigations in other countries for leaks there,” Dr. Ryan said.
He said, however, that Chinese scientists had reported beginning some of the follow-up studies recommended by the international expert team.
The editorial on Wednesday also raised concerns about delays at the W.H.O. The organization said this month that it would form an advisory group to study the emergence of new pathogens, and that the group would support inquiries into the coronavirus. The editorial warned that this new layer of bureaucracy “runs the risk of adding several months of delay.”
Dr. Tedros, the organization’s director-general, said on Wednesday that establishing the advisory group “will not delay the progress of the studies into the origins of SARS-CoV-2.”
The W.H.O. said that it was already orking to verify studies into the earliest known cases outside China.