A lab leak was once dismissed by many as a conspiracy theory. But the idea is gaining traction, even as evidence builds that the virus emerged from a market.WASHINGTON — In the spring of 2021, with studies of the coronavirus pandemic’s origins going nowhere and the issue embroiled in bitter partisan politics, David Relman, a microbiologist at Stanford, quietly made a request of his congresswoman.He told his representative, Anna Eshoo, that he was organizing a letter from leading scientists calling for an open and independent investigation into the origins of Covid-19 — including into whether it had come from a laboratory in Wuhan, China. He wanted to know if she would publicly endorse the idea.The outreach worked. As soon as the letter appeared online in the prestigious journal Science, Ms. Eshoo became one of the first Democrats in Congress to call for an investigation into the origins of Covid.It was the prelude to a political sea change on the issue: Within weeks, President Biden ordered a top-to-bottom intelligence review of how the pandemic began, which has since come to mixed conclusions.David Relman, a microbiologist at Stanford, who called for an independent investigation into the origins of Covid-19.Jason Henry for The New York TimesThe story of the hunt for Covid’s origin is partly about the stonewalling by China that has left scientists with incomplete evidence, all of it about a virus that is constantly changing. For all the data suggesting that the virus may have jumped into people from wild animals at a Chinese market, conclusive proof remains out of reach, as it does for the competing hypothesis that the virus leaked from a lab.But the story is also about politics and how both Democrats and Republicans have filtered the available evidence through their partisan lenses.Some Republicans grew fixated on idea of a lab leak after former President Donald J. Trump raised it in the early months of the pandemic despite scant evidence supporting it. That turned the theory toxic for many Democrats, who viewed it as an effort by Mr. Trump to distract from his administration’s failings in containing the spread of the virus.The intense political debate, now in its fourth year, has at times turned scientists into lobbyists, competing for policymakers’ time and favor. Dr. Relman is just one of several researchers and like-minded thinkers who has successfully worked the corridors of power in Washington to force journalists, policymakers and skeptical Democrats to take the lab leak idea seriously.But the political momentum has not always aligned with the evidence. Even as the idea of an accidental lab leak has now gained standing in Washington, findings reported last week bolstered the market theory. Mining a trove of genetic data taken from swabs at the Huanan Seafood Wholesale Market in Wuhan in early 2020, virus experts said they found samples containing genetic material from both the coronavirus and illegally traded raccoon dogs. The finding, while hardly conclusive, pointed to an infected animal.The new data from the market suggests that China is holding onto clues that could reshape the debate. But for now, at least, the idea of a lab leak seems to have prevailed in the court of public opinion: Two recent polls show that roughly two-thirds of Americans believe that Covid probably started in a lab.In January 2020, members of the Wuhan Hygiene Emergency Response Team searched the closed Huanan Seafood Wholesale Market in Wuhan.Noel Celis/Agence France-Presse — Getty Images‘Conspiracy Theories’In January 2020, as the virus began circulating in Wuhan, Matthew Pottinger, a deputy national security adviser to Mr. Trump who had worked as a reporter in China, developed suspicions about the Wuhan Institute of Virology, known for its advanced research on bat coronaviruses.Mr. Pottinger quietly made a formal request asking intelligence officials to investigate the new outbreak.In Washington’s polarized ecosystem, the notion that the virus could have come from the Wuhan lab was seeping into public debate. On Capitol Hill, Senator Tom Cotton, Republican of Arkansas, raised the idea in a Senate hearing and on Twitter.Around that same time, according to emails disclosed later, some American virologists privately told health officials, including Dr. Anthony S. Fauci, then the director of the National Institute of Allergy and Infectious Diseases, that the virus could have been engineered in a lab, but required more study.When they examined data, including on naturally occurring viruses that shared critical features with the new virus, they concluded the opposite. In a study, they wrote that the virus was “not a laboratory construct or a purposefully manipulated virus.”The study also said the virus was unlikely to have evolved in the course of certain laboratory experiments. (It did not look closely at whether a scientist collecting or isolating a natural virus could have accidentally released it, a hypothesis for which there remains no direct evidence.)Those findings reinforced the view from a February 2020 letter in The Lancet in which scientists, worried that lab leak fears threatened data sharing from China, condemned “conspiracy theories” about a lab-related origin.President Trump in April 2020, at one of the daily White House coronavirus briefings.Doug Mills/The New York TimesProminent scientists may have been publicly aligned, but the president did not share their view. At the end of April 2020, Mr. Trump announced that he had seen intelligence that supported a lab leak but was “not allowed” to share it. Mr. Pottinger said that he did not recall briefing Mr. Trump on the origins question, and that he did not see the president’s comment coming.Democrats showed little inclination to investigate the pandemic’s origins. Like the president’s references to the “China virus,” his suggestion of a lab leak sounded to them like xenophobia and risked fueling anti-Asian sentiment. They trusted Dr. Fauci, who had said that the evidence strongly suggested that the virus had not been manipulated. (He has since said he is open to the idea of a lab accident.) Ms. Eshoo said his comments made her doubt those espousing a lab leak theory.“It seemed to me that Dr. Fauci, whatever he knew, did not lead him to believe what they were believing,” Ms. Eshoo said.Rep. Anna Eshoo arrives at the Rayburn House Office Building for a hearing in May 2020.Anna Moneymaker/The New York TimesChanging Democrats’ MindsWhen Mr. Biden won the 2020 election, some experts who called for a fuller investigation of the lab leak hypothesis saw an opportunity to persuade Democrats to give the idea a closer look.In December 2020, Jamie Metzl, a biosecurity and technology expert at the Atlantic Council who had worked in the Clinton administration, arranged a private telephone call with Jake Sullivan, the incoming national security adviser. Mr. Metzl made the case, he said, “that a research-related origin was a very real possibility.”Mr. Metzl joined a small group, organized by French and Belgian scientists, who had said the lab leak hypothesis could not be ruled out. The scientists, he said, were having trouble getting letters published in science journals. With Mr. Metzl’s help, the group published its views in news outlets around the world.Around the same time, in March 2021, some virus experts became frustrated by a much-anticipated report on the pandemic’s origins by the World Health Organization and China.The report did not trace Covid cases as far back as experts wanted. And it ranked the idea of the virus being carried to Wuhan on frozen food packages — an improbable scenario, but one that China favored because it could push blame beyond the country’s borders — as more likely than a laboratory incident.There was still no evidence of a lab leak, but so much remained unknown — and China seemed so determined to stand in the way of answers — that more scientists began urging a closer look.Dr. Relman of Stanford organized the letter to Science with other prominent colleagues, including Alina Chan, a scientific adviser at the Broad Institute in Cambridge, Mass., and Jesse Bloom, a virologist at the Fred Hutchinson Cancer Center in Seattle.In August, Mr. Metzl helped plan a private bipartisan briefing for senators about the lab leak hypothesis, where Dr. Relman and Dr. Bloom spoke.“I left the meeting with a much more open mind,” said Senator Richard Blumenthal, Democrat of Connecticut.Market CluesAs backers of the lab leak idea made their case in Congress, Michael Worobey, an evolutionary biologist at the University of Arizona, set out to test those claims. Having once investigated — and helped to discredit — a theory that AIDS came from contaminated polio vaccines, he believed a lab leak was possible and so he signed the Science letter.He first nudged the scientific journal Nature, he said, to request that researchers from the Wuhan Institute of Virology make available genetic sequences of previous coronaviruses they had reported in the journal. They did, and shortly thereafter, in May 2021, posted a study describing those viruses, none of which was closely enough related to the pandemic virus that genetic tinkering could have produced it.Next, Dr. Worobey analyzed the earliest known Covid patients, finding that a disproportionate number had worked at or visited the market.Meanwhile, evidence emerged that live mammals known to spread coronaviruses — including raccoon dogs — were being sold at the Huanan market before the pandemic. And in September 2021, a report of coronaviruses recently discovered in Laotian bats showed that naturally occurring viruses were capable of latching onto human cells.Michael Worobey, an evolutionary biologist at the University of Arizona who studied the origins of Covid after calling for an open investigation of all hypotheses.University of ArizonaNew information about the work of the Wuhan Institute of Virology was also intensifying concerns about a lab leak, even as hard evidence of such an incident remained elusive.To some scientists, the institute’s efforts to study never-before-seen coronaviruses raised questions about what else it might have collected. Those questions turned more pointed with news in the fall of 2021 that EcoHealth Alliance, a research organization, had sought Defense Department funding in 2018 to partner with the virology institute on experiments that would have genetically altered coronaviruses.The proposal was not funded. But the concerns fueled Republican attacks on Dr. Fauci for his institute’s funding of other EcoHealth projects and drew attention to the lab leak theory.Richard Ebright, a molecular biologist at Rutgers University who had publicly argued that a lab leak should be considered, said he helped Congressional aides vet questions that Senator Rand Paul, a Republican, wanted to ask Dr. Fauci at upcoming hearings. And Dr. Relman said that he tried to help Republicans on the House Energy and Commerce Committee, who were examining the research, find common ground with Democrats.Congressional inquiries gained steam even as Dr. Worobey’s research leaned toward a market origin. In February 2022, he and others reported that the clustering of early Covid cases around the Huanan market could not be explained purely by chance. A second study by the team, looking at the genetic diversity of viruses collected early in the outbreak, also pointed to the market.The studies, published in Science, persuaded many virologists that the notoriously risky wild animal trade had, as on previous occasions in China, ignited a deadly outbreak.But some scientists and lawmakers were unconvinced. In the Senate, aides were many months into a bipartisan investigation of the origins of the pandemic, including the lab leak idea. The resulting report — in a sign of enduring partisan divisions, it was endorsed only by Republicans — said that safety risks at the Wuhan Institute of Virology made a lab leak likely. But it presented no direct evidence to suggest it had actually occurred.Weeks after the report’s release, Republicans won control of the House.Toxic PoliticsJamie Metzl, senior fellow at the Atlantic Council, testifies at a hearing on March 8 with fellow witnesses, from left, Nicholas Wade, former science editor at The New York Times, Paul Auwaerter, a professor at Johns Hopkins School of Medicine, and Robert Redfield, the former director of the Centers for Disease Control and Prevention.T.J. Kirkpatrick for The New York TimesThis month, the new House Subcommittee on the Coronavirus Pandemic convened its first hearing to examine the pandemic’s origins. The market theory was barely discussed.Some scientists saw the hearing as one-sided and rife with scientific inaccuracies. Dr. Ebright, though, saw an opportunity. With House Republicans leading Covid hearings and Democrats holding the Senate by only a slim majority, he hopes to mobilize the public to push for bipartisan Senate hearings on Covid origins.“The political balance is on the knife’s edge,” he said. “A very small amount of advocacy could have significant impact.”Other scientists, though, said that the campaign by lab leak proponents, far from creating a more open discussion, had given rise to such vitriolic attacks that many researchers are reluctant to speak publicly about the issue.The latest raccoon dog data, which virologists said added to compelling evidence for a market origin, created fresh pressure on China to share information that may link Covid’s origin to wild animals. But others said the new findings related to the market, like previous ones, contained holes.“I worry a lot about our jumping on tidbits that are incomplete and cannot be verified,” Dr. Relman said.After three years of divisive politics, Ms. Eshoo said she would like the Covid origins inquiry to be taken out of Congress’s hands and turned over to an independent panel.“If you take partisan politics and you mix that with science,” she said, “it’s a toxic combination.”Kitty Bennett

At its first public hearing, the House Select Subcommittee on the Coronavirus Pandemic plunged into the politically charged debate over the origins of the virus.WASHINGTON — The House panel investigating the origins of the coronavirus pandemic opened its first public hearing on Wednesday with Republicans and their witnesses making an aggressive case that the virus may have been the result of a laboratory leak — a notion that has become the subject of intense political and scientific debate.“There is no smoking gun proving a lab origin hypothesis, but the growing body of circumstantial evidence suggests a gun that, at the very least, is warm to the touch,” said Jamie Metzl, a senior fellow at the Atlantic Council and a former State Department official.Dr. Metzl was one of three witnesses invited by Republicans. The others were Dr. Robert R. Redfield, who served as the director of the Centers for Disease Control and Prevention under President Donald J. Trump, and Nicholas Wade, who was the science editor of The New York Times in the 1990s and left the news organization at the end of 2011.The three have previously said the virus may have accidentally escaped from a laboratory. But they all said on Wednesday that the question of how the virus originated remained an open one, and that it was important to settle the question.Dr. Paul G. Auwaerter, the clinical director of the infectious diseases division at the Johns Hopkins University School of Medicine, testified at the invitation of Democrats.Some proponents of the laboratory leak hypothesis have suggested that it was a biological weapon intentionally engineered by China. But Dr. Redfield, a virologist, said he had concluded that the virus was a result of an accident, and that his view was based “primarily on the biology of the virus itself,” including the fact that it was highly infectious, spawning the rapid evolution of new variants.Scientists have said that ability could very well have evolved through a natural spillover from an animal. They have cited, among other things, coronaviruses found in bats in 2020 that carry a molecular hook on their surface that is very similar to a feature on the virus that causes Covid-19. That hook allows the viruses to latch onto human cells.Dr. Redfield also called for a moratorium on “gain of function” research, which involves tinkering with the genes of viruses in a way that could make them more infectious. Many scientists argue that such research is necessary to help develop vaccines and other medical countermeasures that could be used in a pandemic.“I disagree with that assessment,” Dr. Redfield said.

In advance of a hearing on Wednesday expected to focus on the lab leak theory, House Republicans took aim at Dr. Anthony S. Fauci, whom they have long vowed to investigate.WASHINGTON — House Republicans on Wednesday will dig into the origins of the coronavirus pandemic in a hearing that promises to be filled with political theater alongside substantive questions about laboratory safety and what, if anything, could have been done to prevent the worst public health crisis in a century.The hearing of the Select Subcommittee on the Coronavirus Pandemic is expected to focus largely on the intensifying debate over whether Covid-19 was the result of a laboratory leak. In advance of the session, Republicans issued a memorandum critical of Dr. Anthony S. Fauci, the former director of the National Institute of Allergy and Infectious Diseases and a leader in the federal response to the pandemic.Republicans have invited three witnesses: Dr. Robert R. Redfield, who served as the director of the Centers for Disease Control and Prevention under President Donald J. Trump; Jamie Metzl, a senior fellow at the Atlantic Council; and Nicholas Wade, who served as science editor for The New York Times in the 1990s and left the news organization at the end of 2011. All have said the virus may have accidentally escaped from a laboratory.Although the lab leak theory has received support from a minority of American intelligence agencies, it recently gained a boost after new intelligence led the Energy Department to conclude, albeit with low confidence, that the pandemic was most likely caused by a laboratory accident.The F.B.I. also believes that the cause of the pandemic was “most likely a potential lab incident,” the bureau’s director, Christopher A. Wray, confirmed last week. But four other intelligence agencies, as well as the National Intelligence Council, have concluded, also with low confidence, that the virus most likely originated in animals and then spread naturally to humans. The C.I.A. has not taken a position.Separately on Wednesday, senior intelligence officials are expected to update senators about their ongoing investigation into the cause of the pandemic, as part of an annual hearing on worldwide threats to national security. Avril D. Haines, the director of national intelligence, will probably face questions about the varying positions intelligence agencies have taken on the issue.Because China has withheld evidence, scientists may never get to the bottom of what caused the pandemic, said Senator Angus King, independent of Maine and a member of the Intelligence Committee.“The more important question is, was this somehow purposeful,” Mr. King said. He added, “If it was a leak from a lab, it tells you something, but it doesn’t tell you if it was somehow malicious.”The coronavirus subcommittee in the House is made up of nine Republicans and seven Democrats. Its members include Representative Marjorie Taylor Greene, the Georgia Republican known for her embrace of conspiracy theories, and Representative Ronny Jackson, Republican of Texas, the former White House doctor who made headlines for his rosy assessment of Mr. Trump’s health. The Pentagon’s inspector general later found that he drank on the job and bullied his staff.The chairman of the subcommittee, Representative Brad Wenstrup, Republican of Ohio, and its top Democrat, Representative Raul Ruiz of California, have worked together on legislation in the past. Mr. Wenstrup, a podiatrist, and Mr. Ruiz, an emergency physician, have both said they would like to rise above partisan politics and conduct a thorough inquiry into the pandemic’s origins.A Divided CongressThe 118th Congress is underway, with Republicans controlling the House and Democrats holding the Senate.G.O.P. Road Shows: House Republicans are increasing the budgets of their congressional committees and going out on the road, planning a busy schedule of field hearings to promote their agenda outside of Washington.Resolution of Disapproval: Republicans are scoring wins and dividing Democrats by employing the arcane maneuver to take aim at policies that they oppose and see as political vulnerabilities for Democrats.‘Weaponization’ of Government: The first three witnesses to testify before the new G.O.P.-led House committee investigating the “weaponization” of the federal government have offered little firsthand knowledge of any wrongdoing or violation of the law, according to Democrats on the panel.“This investigation must begin with where and how this virus came about so that we can attempt to ‘predict, prepare, protect, or prevent’ it from happening again,” Mr. Wenstrup said in a statement.The debate over the lab leak theory centers largely around research conducted at the Wuhan Institute of Virology, in the Chinese city where the pandemic began.Hector Retamal/Agence France-Presse — Getty ImagesBut the political dynamics, particularly around the role of Dr. Fauci, may make that impossible. Long before they took over the House, Republicans vowed that they would investigate him if they won control of the chamber.Ms. Greene has gone so far as to call him an “enemy to the world.”The divisive debate over the lab leak theory centers largely around research conducted at the Wuhan Institute of Virology, a Chinese laboratory that studies coronaviruses in the city where the pandemic began.Dr. Fauci is not on the witness list for Wednesday’s hearing; in a brief interview, he said he was not asked to testify. But on Sunday, Republicans on the subcommittee released a memorandum asserting that he had inappropriately pushed for publication of a scientific paper to tamp down the lab leak hypothesis — an accusation he called “false and misleading” in a statement.“I have stated repeatedly that we must keep an open mind as to the origins of the virus, and that the origin of the virus should be the subject of ongoing, thorough and open-minded scientific study that follows the data and evidence wherever it leads,” Dr. Fauci said in the statement. “That remains my goal today.”Dr. Fauci has said he believes the preponderance of the evidence shows that the pandemic originated in nature, although he remains open to the idea of a laboratory leak. The Republican memo spotlighted his actions in early February 2020 — more than a month before Covid-19 was declared a pandemic — and zeroed in on a series of email exchanges among scientists and health officials as they raced to assess the likeliest origin of the virus.Among those included in the email exchanges were Dr. Fauci; Dr. Francis S. Collins, then the director of the National Institutes of Health; Kristian Andersen, a virologist at the Scripps Research Institute in California; and Dr. Jeremy Farrar, a British medical researcher who was then the director of the Wellcome Trust, a charitable organization focused on health research. In December, the World Health Organization announced that Dr. Farrar had been selected as its new chief scientist.In one email that has garnered attention since it was released in 2021, Dr. Andersen wrote that certain features of the virus made him wonder whether it had been engineered in a laboratory. After discussions with other scientists, he said they had found “the genome inconsistent with expectations from evolutionary theory.”“But,” he added, “we have to look at this much more closely and there are still further analyses to be done, so those opinions could still change.”Within a few days, their assessment had indeed changed. The team of scientists investigating the origins wrote in a summary of their findings that the genetic evidence was inconsistent with a virus that had been deliberately engineered; in other words, they were confident that researchers had not intentionally manufactured it.In March 2020, Dr. Andersen and several co-authors published a study in the scientific journal Nature Medicine that described those findings. The study, titled “The Proximal Origin of SARS-CoV-2,” said their analyses showed that the virus was “not a laboratory construct or a purposefully manipulated virus.”The study also said that given the overlap that the authors had found between the coronavirus and related viruses in nature, they “do not believe that any type of laboratory-based scenario is plausible.”Dr. Anthony S. Fauci has said he believes the preponderance of the evidence shows that the pandemic originated in nature, although he remains open to the idea of a laboratory leak.Michael A. McCoy for The New York TimesRepublicans have suggested that Dr. Fauci influenced the scientists’ change of heart and pushed for publication of the proximal origin study in an effort to tamp down the idea of a lab leak — an assertion that both Dr. Fauci and Dr. Andersen have repeatedly denied.Dr. Andersen and other scientists involved in the study have said that their views changed after a few days of intense work. Emails that have since been made public indicate that they consulted with virologists who had more experience studying coronaviruses and who said that the features that may initially have looked worrisome did not in fact suggest that the virus had been concocted in a lab.Some of those features of the virus were also identified in related coronaviruses in other species, strengthening the view that the features were not necessarily lab-made.Dr. Andersen said that the Republican memo represented a turn away from scientific discussions of the virus’s origins. “I find it deeply problematic how far away from the science we have gotten in our effort to more fully understand the origin of the pandemic,” he said.The Republican memo claimed that the subcommittee had evidence that Dr. Fauci had swayed the study, citing an email from Dr. Andersen to the scientific journal Nature that said Dr. Fauci, among others, had “prompted” their effort “to provide agnostic and scientifically informed hypothesis around the origins of the virus.”Dr. Fauci said in the statement that he did not prompt the drafting of any article intended to rule out a laboratory leak and was not involved in drafting or editing of any portion of the published study. “My only goal,” he wrote, “was to encourage the expert virologists to evaluate the origin of the Covid-19 virus by providing an objective and scientifically sound examination of the information available at the time.”How much attention the Republicans’ memo will garner at Wednesday’s hearing is unclear. None of the witnesses invited by Republicans were involved in the email exchanges in question.Democrats on the subcommittee have invited Dr. Paul G. Auwaerter, the clinical director of the infectious diseases division at the Johns Hopkins University School of Medicine, to testify as well.In a statement, Mr. Ruiz, the top Democrat on the panel, called on Republicans to avoid “politicization, extreme partisan rhetoric and conspiratorial accusations that vilify our nation’s public health experts,” and he urged them to let “the science and facts lead the way.”Julian E. Barnes

Scientists and spy agencies have tried to determine where the coronavirus originated, but conclusive evidence is hard to come by and the nation’s intelligence agencies are split.WASHINGTON — The Energy Department’s conclusion, with “low confidence,” that an accidental laboratory leak in China most likely caused the coronavirus pandemic has renewed questions about what sparked the worst public health crisis in a century — and whether the virus at the heart of it was somehow connected to scientific research.Scientists and spy agencies have tried assiduously to answer that question, but conclusive evidence is hard to come by. The nation’s intelligence agencies are split, and none of them changed their conclusions after seeing the Energy Department’s findings, officials said.Scientists who have studied the genetics of the virus, and the patterns by which it spread, say the most likely cause is that the virus jumped from live mammals to humans — a scientific phenomenon known as “zoonotic spillover” — at the Huanan Seafood Wholesale Market in Wuhan, China, the city in which the first cases of Covid-19 emerged in late 2019.But other scientists say there is evidence, albeit circumstantial, that the virus came from a lab, possibly the Wuhan Institute of Virology, which had deep expertise in researching coronaviruses. Lab accidents do happen; in 2014, after accidents involving bird flu and anthrax, the Centers for Disease Control and Prevention tightened its biosafety practices.The debate is politically fraught. The lab leak theory gained currency among Republicans in the spring of 2020 after President Donald J. Trump, who used inflammatory terms to blame China for the pandemic, latched onto the idea. Many Democrats have not been persuaded by the lab leak hypothesis; some say they believe the explanation of natural causes, and others say there may never be enough intelligence to draw a conclusion.The Energy Department’s findings have given a boost to House Republicans, who are investigating the pandemic’s origins. But apart from the politics, experts say that understanding what caused a public health crisis that has killed nearly seven million people could help researchers understand how to prevent the next one.Here’s what we know, and don’t know, about the origins of the coronavirus.Why is it hard to know for certain how the pandemic started?It is often difficult to find the origins of viruses, but China has compounded that problem by making it very difficult to gather evidence.Covid-19 in ChinaThe decision by the Chinese government to cast aside its restrictive “zero Covid” policy at the end of 2022 set off an explosive Covid outbreak.A Receding Wave: Two months after China abandoned its Covid rules, the worst seems to have passed, and the government is eager to shift attention to economic recovery.Death Toll: While a precise accounting is impossible, rough estimates suggest that between 1 and 1.5 million people died of Covid during China’s wave — far more than the official count.Digital Finger-Pointing: The Communist Party’s efforts to limit discord over its sudden “zero Covid” pivot are being challenged with increasing rancor on the internet.By the time Chinese researchers arrived to collect samples from the Huanan market, the police had shut down and disinfected the market because a number of people linked to it had become sick with what would later be recognized as Covid. No live market animals were left.Some scientists also believe that China has provided an incomplete picture of early Covid cases. And they worry that a directive to hospitals early in the outbreak to report illnesses specifically linked to the market may have led doctors to overlook other cases with no such ties, creating a biased snapshot of the spread.What have scientists done to investigate?Experts have tried to work around the holes in the data.Scientists have examined cases of patients hospitalized before the call went out for doctors to look for ties to the market. They have also mapped the locations of early Covid cases in Wuhan — including both people who were initially linked to the market and those who were not — and found what they say are signs that the virus started spreading at the market.Some of those same scientists have studied maps of where investigators found the virus in the Huanan market, including walls, floors and other surfaces, and found that those samples clustered in an area of the market where live animals were sold.And separate genetic analyses from the very early stages of the pandemic, some scientists have said, suggest that the virus spilled over into people working or shopping at the market on two separate occasions.Other scientists have disputed that studies like those can indicate a market origin with much confidence. They have said, for example, that the evidence for two separate spillovers at the market could also be evidence of the virus evolving as it spread from person to person..css-1v2n82w{max-width:600px;width:calc(100% – 40px);margin-top:20px;margin-bottom:25px;height:auto;margin-left:auto;margin-right:auto;font-family:nyt-franklin;color:var(–color-content-secondary,#363636);}@media only screen and (max-width:480px){.css-1v2n82w{margin-left:20px;margin-right:20px;}}@media only screen and (min-width:1024px){.css-1v2n82w{width:600px;}}.css-161d8zr{width:40px;margin-bottom:18px;text-align:left;margin-left:0;color:var(–color-content-primary,#121212);border:1px solid var(–color-content-primary,#121212);}@media only screen and (max-width:480px){.css-161d8zr{width:30px;margin-bottom:15px;}}.css-tjtq43{line-height:25px;}@media only screen and (max-width:480px){.css-tjtq43{line-height:24px;}}.css-x1k33h{font-family:nyt-cheltenham;font-size:19px;font-weight:700;line-height:25px;}.css-1hvpcve{font-size:17px;font-weight:300;line-height:25px;}.css-1hvpcve em{font-style:italic;}.css-1hvpcve strong{font-weight:bold;}.css-1hvpcve a{font-weight:500;color:var(–color-content-secondary,#363636);}.css-1c013uz{margin-top:18px;margin-bottom:22px;}@media only screen and (max-width:480px){.css-1c013uz{font-size:14px;margin-top:15px;margin-bottom:20px;}}.css-1c013uz a{color:var(–color-signal-editorial,#326891);-webkit-text-decoration:underline;text-decoration:underline;font-weight:500;font-size:16px;}@media only screen and (max-width:480px){.css-1c013uz a{font-size:13px;}}.css-1c013uz a:hover{-webkit-text-decoration:none;text-decoration:none;}How Times reporters cover politics. We rely on our journalists to be independent observers. So while Times staff members may vote, they are not allowed to endorse or campaign for candidates or political causes. This includes participating in marches or rallies in support of a movement or giving money to, or raising money for, any political candidate or election cause.Learn more about our process.Some have also argued that for all the attention being paid to the Wuhan Institute of Virology, not enough has been paid to a different research site in the city, the Wuhan Center for Disease Control and Prevention. That center is much closer to the Huanan market.Why do some people suspect a laboratory leak?In October, Republicans on the Senate health committee published an analysis of the origins of the pandemic that argued it was “most likely the result of a research-related incident,” while acknowledging that the conclusion was “not intended to be dispositive.”The report spotlighted what its authors described as holes in the natural origins theory, as well as “persistent biosafety problems” at the Wuhan Institute of Virology. The report, though, relied largely on existing public evidence, rather than new or classified information, and did not produce evidence to show that the Wuhan institute stored any virus in its collections that could have become the virus causing Covid-19, with or without scientific tinkering.The lab leak hypothesis is bolstered, the report said, by the absence of any published evidence that SARS-CoV-2, the virus that causes Covid-19, was circulating in animals before the pandemic. Samples of virus collected on refrigerators, countertops and other surfaces at the Huanan market were genetically similar to human samples, suggesting the virus was shed by humans, not animals, it said.But some experts said the inability to find an infected animal did not prove anything, because China shut down the market and killed all of its animals before they could be tested.In 2018, before the pandemic, the Wuhan institute and its partners — including EcoHealth Alliance, a research group whose work has been financed by the United States — sought Defense Department funding to collect and experiment on coronaviruses with novel traits that would make them highly transmissible in humans.The group project was never funded. But the report pointed to that proposal, noting that the virus that causes Covid-19 has traits similar to what the researchers were looking for. That has persuaded some scientists that a lab leak was possible. The Senate Republican report surmised that the virus may have escaped — perhaps by infecting a researcher who then carried it outside the lab.The National Institutes of Health paid for some of EcoHealth Alliance’s work in Wuhan, but N.I.H. officials have repeatedly said the viruses being studied with American taxpayer dollars bore no genetic resemblance to the one that causes Covid-19. But Dr. Lawrence A. Tabak, the N.I.H.’s acting director, acknowledged during a recent congressional hearing that he did not know what other work the Wuhan institute was doing.What does the American intelligence community say?In May 2021, several months after he took office, President Biden ordered the nation’s intelligence agencies to conduct a 90-day inquiry into the cause of the pandemic. The findings of that review were released in August 2021 and reaffirmed what the agencies had previously said: Both the natural origins theory and the lab leak theory were plausible.In a statement at the time, Mr. Biden called on China to be more transparent about what had led to the emergence of the virus there in late 2019.The Energy Department’s new conclusion is based on intelligence that is not publicly available, so it is difficult to know what accounted for the change. But the department’s use of the phrase “low confidence” indicates that its level of certainty is not high. The F.B.I., however, has concluded with “moderate confidence” that the virus emerged accidentally from a lab.Four other intelligence agencies and the National Intelligence Council have concluded, with low confidence, that the virus most likely emerged through natural transmission. The C.I.A., the nation’s pre-eminent spy agency, has not taken a position and remains undecided.What is Congress doing to address the question?House Republicans have been trying to investigate the origins of the pandemic and gather evidence that might shed light on what caused it — including whether China concealed facts about the initial outbreak and what research American tax dollars may have financed in Wuhan.Now that Republicans are in charge of the House, that investigative work is escalating in several committees, including the Intelligence Committee, the Energy and Commerce Committee and the Select Subcommittee on the Coronavirus Pandemic. The subcommittee will hold its first hearing on the origins question on March 8, a spokeswoman said.