The mouse infected with a lab-created type of SARS coronavirus was squirming upside down, dangling by its tail as a scientist carried it to a weighing container one day in February 2016. But the mundane task turned dangerous in seconds inside the North Carolina laboratory, which has drawn scrutiny for its partnership on similar research with China’s Wuhan Institute of Virology.

In that moment, it wasn’t enough that the experiment was taking place inside a biosafety level 3 lab, the second-highest security level, which was layered in high-tech equipment designed to keep dangerous pathogens from escaping. Or that the scientist was covered head-to-toe in gear to protect against infection: a full-body Tyvek suit, boot covers and double gloves, plus a powered air-purifying respirator.

As she carried the mouse, it climbed up its tail and bit her hard, breaking through the gloves and plunging its teeth — and potentially the virus — into her ring finger.

Then, instead of quarantining to wait for signs of infection, the scientist was allowed to go about her life in public for the next 10 days, wearing a surgical mask and reporting her temperature twice daily, newly obtained records show.

The scientist ultimately did not become ill, but the 2016 safety breach at the University of North Carolina at Chapel Hill’s high-containment laboratories is one of several near-miss incidents at the university in recent years involving multiple types of genetically engineered coronaviruses, the records show.

While no one is suggesting that UNC created the virus that causes COVID-19, alone or with the Wuhan lab, such near misses highlight the potential risks of an infected lab worker exposing the public even in the most secure and respected research facilities as they search for treatments and vaccines.

The university has declined to publicly disclose key details about the incidents, including the names of viruses involved, the nature of the modifications made to them and what risks were posed to the public, contrary to National Institutes of Health guidelines.

“The University notified the proper oversight agencies about the incidents and took corrective action as needed,” UNC said in a statement, noting that its research has contributed to promising treatments for COVID-19. “It is absolutely critical to understand what viruses exist in nature and how they could affect human health.”

The nature of the safety breaches at UNC are particularly important now as the origins of COVID-19, which has killed more than 775,000 people worldwide and infected 21.7 million others, continue to elude public health officials and other investigators.

President Donald Trump and Secretary of State Mike Pompeo have publicly speculated, without offering proof, that a lab in Wuhan, the Chinese city where COVID-19 cases first appeared, may be responsible for the current coronavirus pandemic. While that theory is dismissed by many as political blame-shifting and anti-China rhetoric, credible scientists have been concerned for years about the potential for a lab accident to cause a pandemic.

Richard Ebright, a molecular biologist at Rutgers University who has testified before Congress on lab safety issues, said the series of incidents with coronaviruses at UNC gives fuel to the possibility that this pandemic, or one in the future, could originate as a lab accident.

Since 2007, the U.S. Government Accountability Office, the investigative arm of Congress, has repeatedly warned that the proliferation of high-containment biosafety level 3 and level 4 labs in the United States and around the world is increasing the risk of dangerous viruses, bacteria or toxins being intentionally or unintentionally released from the facilities. Over the years, Congress has held multiple hearings examining numerous serious incidents in elite U.S. labs, including mishaps with anthrax, deadly smallpox and Ebola viruses and dangerous strains of avian influenza.

In April, the Office of the Director of National Intelligence issued a public statement that while the U.S. intelligence community agrees with widespread scientific consensus that the COVID-19 virus was not human-made or genetically modified, federal spy agencies and security organizations have not ruled out a lab accident as the source of the outbreak.

“The IC will continue to rigorously examine emerging information and intelligence to determine whether the outbreak began through contact with infected animals or if it was the result of an accident at a laboratory in Wuhan,” the statement said.

Questions about a potential lab accident have focused on two large infectious disease labs in Wuhan: The Wuhan Institute of Virology and the Wuhan Center for Disease Control and Prevention. The Chinese government has said the labs had nothing to do with the pandemic.

“It is unfortunate that we have been targeted as a scapegoat for the origin of the virus,” Wang Yanyi, director of the Wuhan Institute of Virology said in an interview this month with NBC News.

The Wuhan Institute of Virology is China’s first research facility to operate biosafety level 4 labs, the highest safety level, which are built with special design features and equipment to prevent the most dangerous pathogens from getting out. The institute has specialized in the study of bat coronaviruses, research led by virologist Shi Zhengli, who has been nicknamed the “Bat Woman” for her team’s pursuit of specimens of wild SARS-like viruses in bat caves.

In July, Shi fired back at White House speculation about the institute, telling Science magazine that the institute had never had contact with or studied the virus that causes COVID-19 until Dec. 30, 2019, when it first received samples from patients who were sickened with an unknown type of pneumonia. “U.S. President Trump’s claim that SARS-CoV-2 was leaked from our institute totally contradicts the facts,” she told Science.

Researchers like Shi and the team of scientists at UNC are attempting to determine which of the many coronaviruses that currently only infect animals have the potential to mutate in ways that would allow them to jump to humans, allowing for advance development of treatments and vaccines.

The February 2016 safety breach at the UNC’s high-containment laboratories drew scrutiny at the time from concerned federal health officials, records show. In its aftermath, UNC officials provided repeated updates to the Centers for Disease Control and Prevention, though neither the university nor the CDC will say what they were about. The university deleted the virus name from incident reports it released in response to a public records request. Federal lab safety officials at the NIH confirmed in an emailed response to questions from ProPublica that the 2016 incident, as well as several others where UNC redacted the pathogen name from reports, involved types of “SARS-associated Coronavirus.” But the NIH, which oversees experiments involving genetically modified viruses and bacteria, did not provide any further details about the nature or genetic composition of the lab-created viruses.

NIH, CDC and UNC officials declined to explain the potential risks to the public of the 2016 incident or why the researcher wasn’t quarantined until it was known she wasn’t infected. NIH said it is each research institution’s responsibility to assess the risks of an incident and respond to it appropriately.

After the researcher was bitten by the infected mouse, university officials initially discussed “options for isolation” of the scientist during the incubation period for the lab-created virus, the incident reports show. Instead, they allowed her to remain in public, only requiring that she wear a surgical mask and report her temperature twice daily.

While the researcher did not get sick, the case underscores the concerns that have been raised about the potential for a lab accident to unleash a dangerous virus — natural or human-made — into the surrounding community and beyond. It also illustrates how potentially infected lab workers could be allowed to move about in a city and the efforts that labs make to keep details of such safety breaches secret.

Records show that during the five years before the pandemic began, at least six UNC researchers were required to undergo medical monitoring following four incidents where they were potentially exposed to what the NIH now confirms were types of lab-created SARS coronaviruses. In addition, two other UNC researchers had to undergo medical surveillance because of their potential exposure to a type of lab-created MERS coronavirus. The monitoring involved reporting temperatures or any symptoms to university medical officials twice daily.

In each case, the reports indicate these workers were allowed to go about their lives while waiting for symptoms to appear. As the world has learned in recent months, it’s possible for people without symptoms to be infected with the coronavirus and unknowingly spread disease to others.

Safety incidents at UNC have continued in the wake of the pandemic as the university’s researchers have joined scientists worldwide studying the new SARS-CoV-2 virus that causes COVID-19.

On April 21, a UNC researcher wearing full-body protective gear was bitten on their index finger while weighing a mouse infected with a genetically altered form of the SARS-CoV-2 virus adapted to grow in mice. In contrast to the 2016 mouse mishap, the researcher bitten this spring was told to self-quarantine at home for 14 days, records show. The local Health Department was also notified about the incident.

UNC officials declined to be interviewed and did not answer questions about the incidents sent to them in writing.

Research at UNC’s biosafety level 3 labs has come under scrutiny in the past because of controversial coronavirus experiments its scientists have done with partners at the Wuhan Institute of Virology.

In November 2015, UNC scientists published a research paper detailing how they had created a lab-made hybrid coronavirus with the potential to infect people. Their experiments involved inserting part of a coronavirus called SHC014-CoV found in Chinese horseshoe bats into a SARS virus to see if the lab-made hybrid virus — called a chimera — could efficiently infect human cells.

It could. And it prompted the research team — which included scientists at the Wuhan Institute of Virology — to warn in their paper of the risks that the SHC014 coronavirus and others circulating in bat populations have to potentially emerge as a threat to humans. At UNC, a senior author of the paper was Ralph Baric, an epidemiology professor and international expert on coronaviruses. UNC said Baric was unavailable for an interview, but it noted the virus in the experiment was “a very different strain” than the one that causes COVID-19.

The potential risks posed by creating a virus not found in nature prompted criticism at the time from some scientists. The paper added to an ongoing international debate over risks and benefits of creating genetically modified pathogens that are potentially more dangerous than what’s found in nature, what’s known as “gain of function” research.

“If the virus escaped, nobody could predict the trajectory,” Simon Wain-Hobson, a virologist at the Pasteur Institute in Paris, told Nature at the time the UNC paper was published.

UNC officials would not say whether the 2016 mouse-bite incident, which occurred three months after the paper was published, involved a SARS chimera virus like the one in the 2015 paper.

Experts who reviewed the incident reports at ProPublica’s request said it is difficult to gauge the risks of UNC’s coronavirus incidents because the university removed key details about the nature of the viruses involved.

“There is no reason for the public not to be informed about the nature of biological agents involved in lab research and accidents,” said Gregory Koblentz, director of the biodefense graduate program at George Mason University, who noted that the research is not classified and will eventually be published in scientific journals.

“Making these reports public ensures accountability for the labs and funders and encourages them to learn from mistakes and reduce risk of them occurring,” Koblentz said.

UNC is required as a condition of its federal research funding to release to the public on demand certain safety records, including incident reports, about its work with genetically modified viruses. After ProPublica filed a complaint about UNC’s removal of the virus names, NIH said it contacted UNC “to remind them of their obligations.” But UNC still didn’t release the pathogen names and genetic modifications it removed from the records.

While UNC wouldn’t discuss the 2016 incident, in its statement to ProPublica the university emphasized that the research for the 2015 paper was approved by NIH, that it followed all safety protocols and that it was deemed a “low-risk” experiment because of the strain of coronavirus being studied.

“It is because of our early work that the United States was in a position to quickly find the first successful treatment for SARS-CoV-2,” the university said in its statement. Research by UNC scientists has contributed to the development of a drug called EIDD-2801, which shows promise in preventing lung damage from COVID-19.

The source of the current pandemic remains unknown. Many scientific experts believe the virus that causes COVID-19 emerged in nature and is the result of people being exposed to bats or another type of animal that are natural carriers of it. Experts who have studied the virus’s genetic sequence have said it doesn’t appear to be genetically engineered.

Coronaviruses have jumped from animals to humans before. In 2002, the SARS coronavirus that causes severe acute respiratory syndrome emerged possibly from bats in southern China to set off an international epidemic that was extinguished in 2003 through public health measures. In 2012, the MERS coronavirus that causes Middle East respiratory syndrome was first identified in people sickened in Saudi Arabia and other countries in and near the Arabian Peninsula. It has been linked to exposure to camels.

But for the COVID-19 virus causing the current pandemic, more study is needed to know where and how the virus jumped from animals to humans.

“There have been extensive discussions about why the virus is almost certainly a naturally occurring strain, but the origin of the outbreak can only be determined — if it can ever be determined — by going through that more medical chain and examining those records,” said Gigi Kwik Gronvall, a senior scholar at the Johns Hopkins Center for Health Security.

While rare, outbreaks that spread from labs to people or animals in the surrounding environment have happened.

A lab accident or mishap with a vaccine trial are considered to be likely explanations for how a strain of flu that appeared to have been genetically frozen in time since the 1950s emerged and infected people around the world in 1977-78.

In 2004, a small outbreak of severe acute respiratory syndrome was traced by Chinese authorities and the World Health Organization to lab workers at the National Institute of Virology Laboratory of China’s Center for Disease Control in Beijing, where experiments were conducted using live and inactivated SARS coronavirus. And in 2007, leaking drainage pipes at a vaccine research facility in England were blamed for an outbreak of foot and mouth disease among cattle.

For now, a team of experts from the World Health Organization is investigating the pandemic’s origins, with a focus on understanding the animal hosts for COVID-19 and how the disease jumped between animals and humans.

“Identifying the origin of emerging viral disease has proven complex in past epidemics in different countries,” the WHO said in a statement last month. “The process is an evolving endeavor which may lead to further international scientific research and collaboration globally.”