NEW YORK — To a growing chorus of US politicians and scientists, she is the key to whether the world will ever learn if the virus behind the devastating Covid-19 pandemic escaped from a Chinese lab. To the Chinese government and public, she is a hero of the country’s success in curbing the epidemic and a victim of malicious conspiracy theories.

Dr Shi Zhengli, a top Chinese virologist, is once again at the centre of clashing narratives about her research on coronaviruses at a state lab in Wuhan, the city where the pandemic first emerged.

The idea that the virus may have escaped from a lab had long been widely dismissed by scientists as implausible and shunned by others for its connection with former US President Donald Trump.

But fresh scrutiny from the Biden administration and calls for greater candour from prominent scientists have brought the theory back to the fore.

Scientists generally agree that there is still no direct evidence to support the lab leak theory. But more of them now say that the hypothesis was dismissed too hastily, without a thorough investigation, and they point to a range of unsettling questions.

Some scientists say Dr Shi conducted risky experiments with bat coronaviruses in labs that were not safe enough. Others want clarity on reports, citing US intelligence, suggesting that there were early infections of Covid-19 among several employees of the Wuhan Institute of Virology.

Dr Shi has denied these accusations and now finds herself defending the reputation of her lab and, by extension, that of her country. Reached on her cellphone two weeks ago, Dr Shi said at first that she preferred not to speak directly with reporters, citing her institute’s policies. Yet she could barely contain her frustration.

“How on earth can I offer up evidence for something where there is no evidence?” she said, her voice rising in anger during the brief, unscheduled conversation. “I don’t know how the world has come to this, constantly pouring filth on an innocent scientist,” she wrote in a text message.

In a rare interview over email, she denounced the suspicions as baseless, including the allegations that several of her colleagues may have been ill before the outbreak emerged.

The speculation boils down to one central question: Did Dr Shi’s lab hold any source of the new coronavirus before the pandemic erupted? Dr Shi’s answer is an emphatic no.

But China’s refusal to allow an independent investigation into her lab, or to share data on its research, make it difficult to validate Dr Shi’s claims and has only fueled nagging suspicions about how the pandemic could have taken hold in the same city that hosts an institute known for its work on bat coronaviruses.

Those in favour of the natural origins hypothesis, though, have pointed to Wuhan’s role as a major transportation hub as well as a recent study that showed that just before the pandemic hit, the city’s markets were selling many animal species capable of harbouring dangerous pathogens that could jump to humans.

The Chinese government has given no appearance of holding Dr Shi under suspicion. Despite the international scrutiny, she seems to have been able to continue her research and give lectures in China.

The stakes in this debate extend into how scientists study infectious diseases. Some scientists have cited the lab leak scenario in pushing for greater scrutiny of “gain of function” experiments that, broadly defined, are intended to make pathogens more powerful to better understand their behaviour and risks.

Many scientists say they want the hunt for the virus’ origins to transcend politics, borders and individual scientific achievements.

“This has nothing to do with fault or guilt,” said Dr David Relman, a microbiologist at Stanford University and co-author of a recent letter in the journal Science, signed by 18 scientists, that called for a transparent investigation into all viable scenarios, including a lab leak.

The letter urged labs and health agencies to open their records to the public.

“It’s just bigger than any one scientist or institute or any one country — anybody anywhere who has data of this sort needs to put it out there,” Dr Relman said.

‘Transparency matters.’

Many virologists maintain that the coronavirus most likely jumped from an animal to a human in a setting outside a lab. But without direct proof of a natural spillover, more scientists and politicians have called for a full investigation into the lab leak theory.

Proponents of a lab investigation say that researchers at Dr Shi’s institute could have collected — or contracted — the new coronavirus from the wild, such as in a bat cave. Or the scientists may have created it, by accident or by design. Either way, the virus could then have leaked from the laboratory, perhaps by infecting a worker.

China has sought to influence investigations into the virus’ origin, while promoting its own unproven allegations.

Beijing agreed to allow a team of World Health Organization (WHO) experts to visit China but limited their access.

When the WHO team said in a report in March that a lab leak was extremely unlikely, its conclusion was seen as hasty. Even the head of the WHO, Dr Tedros Adhanom Ghebreyesus, said: “I do not believe that this assessment was extensive enough.”

Last month, US President Joe Biden ordered intelligence agencies to investigate the origin question, including the lab theory.

On Sunday, the leaders of the world’s wealthiest large democracies, at the Group of 7 summit, urged China to be part of a new investigation into the origins of the coronavirus. Mr Biden told reporters that he and other leaders had discussed access to labs in China.

“Transparency matters across the board,” Mr Biden said.

‘Scientists have a motherland.’

In less polarised times, Dr Shi was a symbol of China’s scientific progress, the “Bat Woman” at the forefront of research into emerging viruses.

She led expeditions into caves to collect samples from bats and guano, to learn how viruses jump from animals to humans. In 2019, she was among 109 scientists elected to the American Academy of Microbiology for her contributions to the field.

“She’s a stellar scientist — extremely careful, with a rigorous work ethic,” said Dr Robert C Gallo, director of the Institute of Human Virology at the University of Maryland School of Medicine.

The Wuhan Institute of Virology employs nearly 300 people and is home to one of only two Chinese labs that have been given the highest security designation, Biosafety Level 4. Dr Shi leads the institute’s work on emerging infectious diseases, and over the years, her group has collected over 10,000 bat samples from around China.

Dr Shi, 57, obtained her PhD from the University of Montpellier in France in 2000 and started studying bats in 2004 after the outbreak of severe acute respiratory syndrome, or Sars, which killed more than 700 people around the world.

In 2011, she made a breakthrough when she found bats in a cave in southwestern China that carried coronaviruses that were similar to the virus that causes Sars.

“In all the work we do, if just once you can prevent the outbreak of an illness, then what we’ve done will be very meaningful,” she told CCTV, China’s state broadcaster, in 2017.

But some of her most notable findings have since drawn the heaviest scrutiny. In recent years, Dr Shi began experimenting on bat coronaviruses by genetically modifying them to see how they behave.

In 2017, she and her colleagues at the Wuhan lab published a paper about an experiment in which they created new hybrid bat coronaviruses by mixing and matching parts of several existing ones — including at least one that was nearly transmissible to humans — in order to study their ability to infect and replicate in human cells.

Proponents of this type of research say it helps society prepare for future outbreaks. Critics say the risks of creating dangerous new pathogens may outweigh potential benefits.

The picture has been complicated by new questions about whether US government funding that went to Dr Shi’s work supported controversial gain-of-function (GOF) research.

The Wuhan institute received around $600,000 in grant money from the US government, through an American nonprofit called EcoHealth Alliance. The National Institutes of Health said it had not approved funding for the nonprofit to conduct GOF research on coronaviruses that would have made them more infectious or lethal.

Dr Shi, in an emailed response to questions, argued that her experiments differed from GOF work because she did not set out to make a virus more dangerous but to understand how it might jump across species.

“My lab has never conducted or cooperated in conducting GOF experiments that enhance the virulence of viruses,” she said.

‘Speculation rooted in utter distrust.’

Concerns have centered not only on what experiments Dr Shi conducted but also on the conditions under which she did them.

Some of Dr Shi’s experiments on bat viruses were done in Biosafety Level 2 labs, where security is lower than in other labs at the institute. That has raised questions about whether a dangerous pathogen could have slipped out.

Ralph Baric, a University of North Carolina expert in coronaviruses who signed the open letter in Science, said that although a natural origin of the virus was likely, he supported a review of what level of biosafety precautions were taken in studying bat coronaviruses at the Wuhan institute. Baric conducted NIH-approved GOF research at his lab using information on viral genetic sequences provided by Dr Shi.

Dr Shi said that bat viruses in China could be studied in BSL-2 labs because there was no evidence that they directly infected humans, a view supported by some other scientists.

She also rejected recent reports that three researchers from her institute had sought treatment at a hospital in November 2019 for flu-like symptoms, before the first Covid-19 cases were reported.

“The Wuhan Institute of Virology has not come across such cases,” she wrote. “If possible, can you provide the names of the three to help us check?”

As for samples that the lab held, Dr Shi has maintained that the closest bat virus she had in her lab, which she shared publicly, was only 96 per cent identical to Sars-CoV-2, the virus that causes Covid-19 — a vast difference by genomic standards. She rejects speculation that her lab had worked on other viruses in secret.

Dr Shi’s research on a group of miners in Yunnan province who suffered severe respiratory disease in 2012 has also drawn questions. The miners had worked in the same cave where Dr Shi’s team later discovered the bat virus that is close to Sars-CoV-2.

Dr Shi said that her lab did not detect bat Sars-like coronaviruses in the miners’ samples and that she would publish more details in a scientific journal soon; her critics say she has withheld information.

“This issue is too important not to come forward with everything you have and in a timely and transparent manner,” said Dr Alina Chan, a postdoctoral research fellow at the Broad Institute of MIT and Harvard who also signed the Science letter.

Many scientists and officials say China should share employees’ medical records and the lab’s logs of its experiments and its viral sequence database to evaluate Dr Shi’s claims.

Dr Shi said she and the institute had been open with the WHO and with the global scientific community.

“This is no longer a question of science,” she said on the phone. “It is speculation rooted in utter distrust.”

‘I have nothing to fear.’

The pandemic was a moment that Dr Shi and her team had long braced for. For years, she had warned of the risks of a coronavirus outbreak, building up a stock of knowledge about these pathogens.

In January 2020, as Dr Shi and her team worked frantically, they were exhausted but also excited, said Dr Wang Linfa, a virologist at the Duke-National University of Singapore Medical School who was in Wuhan with Dr Shi at the time.

“All the experiences, reagents and the bat samples in the freezer were finally being used in a significant way globally,” said Dr Wang, Dr Shi’s collaborator and friend for 17 years.

Dr Shi published some of the most important early papers on Sars-CoV-2 and Covid-19, which scientists around the world have relied on.

But soon, the speculation about Dr Shi and her lab began to swirl. Dr Shi, who is known among friends for being blunt, was baffled and angry — and sometimes let it show.

In an interview with Science magazine in July, she said that Mr Trump owed her an apology for claiming the virus came from her lab. On social media, she said people who raised similar questions should “shut your stinky mouths.”

Dr Shi said what she saw as the politicisation of the question had sapped her of any enthusiasm for investigating the origins of the virus. She has instead focused on Covid vaccines and the features of the new virus, and over time, she said, has calmed down.

“I’m sure that I did nothing wrong,” she wrote. “So I have nothing to fear.”

This article originally appeared in The New York Times.