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Since the early days of the COVID-19 epidemic, theories have circulated about the origin of the novel coronavirus causing the disease, SARS-CoV-2. One prominent rumor is that it first escaped from a lab in Wuhan studying bat coronaviruses and then spread to the public. This theory has also evolved into claims that the virus was genetically engineered to be a bioweapon. But scientists say that while there’s not enough information to pinpoint where the virus came from, there is no evidence that it was created in a lab.

The lab-escape theory had been circulating on social media and various blogs for weeks, but gained considerable visibility in a New York Post article in late February. In it, Steven Mosher, a social scientist and the president of the Population Research Institute in Front Royal, Virginia, summarizes why he believes SARS-CoV-2 may have been accidentally spread by China’s National Biosafety Laboratory at the Wuhan Institute of Virology, where researchers have studied bat coronaviruses.

In the article, Mosher describes several lines of reasoning, namely, that the lab is less than 10 miles away from the seafood market where a cluster of COVID-19 cases was first discovered, and that after the 2003 SARS outbreak, the SARS-CoV virus escaped from virology labs multiple times in China. He also describes how Chinese virologist and bioweapons expert Major General Chen Wei went to the Wuhan Institute of Virology with military scientists in January to study the new virus, which Mosher sees as a form of damage control.

“The circumstantial evidence surrounding it is pretty compelling. . . . The idea that the epicenter of this epidemic would be just a few miles from the Institute of Virology in Wuhan, which is where we know that dangerous pathogens are being kept and looked at as potential bioweapons, I think the odds against that are just astronomical,” Mosher tells The Scientist.

We don’t need to come up with farfetched theories when the genome sequences and the characteristics of these viruses support what we’re seeing. —Paul McCray, University of Iowa

Dimitrios Paraskevis, an epidemiologist at the National and Kapodistrian University of Athens in Greece, tells The Scientist that while it’s not possible to rule out the idea of lab escape, he believes that it is unlikely. “Any person who works in a lab must follow very strict safety regulations. It sounds to me very extraordinary that something happened and nobody took care about such an accident,” he says. The World Health Organization updated SARS surveillance guidelines in 2004 after the lab-based outbreaks, urging labs to follow proper biosafety procedures, and China replaced the director of its Center for Disease Control and Prevention.

One problem leading to a lot of apprehension and speculation about the new coronavirus is that scientists “don’t know what the actual source of the virus was,” Anthony Fehr, a coronavirus researcher at the University of Kansas, tells The Scientist. Additionally, researchers don’t know if SARS-CoV-2 immediately started to spread in humans after a single transmission from an animal, or if it took multiple zoonotic events between an infected animal population and humans.

Despite the question mark around the exact source of the disease, it does appear to have originally come from wildlife, according to a team of international public health scientists who wrote a statement published in The Lancet. An analysis of SARS-CoV-2 by scientists at the Wuhan Institute of Virology suggests that the virus’s genome is 96 percent similar to a coronavirus found in bats.

Mosher agrees that animals were the likely origin. “That doesn’t mean [the virus] wasn’t collected, brought to the lab, and was being tested on in various ways, and escaped from the lab,” he says. Mosher also does not claim that China genetically engineered the virus. “I’m not saying this has been genetically engineered to be a bioweapon that’s escaped from the lab. . . . I’m just saying that [China is] collecting dangerous pathogens, [and] they have a history of letting them escape from the lab,” he says.

Transmission from an animal, with no lab experiment or genetic manipulation involved, fits best with what scientists know about how other coronaviruses have made the jump to humans. In the past, these viruses have spread through wild bats that infect another type of animal—an intermediate host—that then spreads it to humans. SARS-CoV, for example, was transmitted from bats to civets to humans, while camels were an intermediate host in MERS, according to Quanta. The civet version of SARS-CoV was 99.8 percent similar to the one found in humans—much more closely related than the bat and human varieties of SARS-CoV-2—so researchers believe the new coronavirus also infected another type of animal on its way from bats to humans. But they have not found a candidate so far, according to Nature.

This ability to move in between different animal hosts is a characteristic feature of coronaviruses, according to Paul McCray, a pulmonologist at the University of Iowa Carver College of Medicine whose lab studies coronaviruses. “It’s exactly what we’ve learned in studies of SARS in 2002 and 2003, and MERS in 2012. . . . So the concept that this is happening again should come as no surprise,” he says. “For people that work with these viruses, this is completely unsurprising. We don’t need to come up with farfetched theories when the genome sequences and the characteristics of these viruses support what we’re seeing.”

No signs of engineering in SARS-CoV-2 genome

In addition to the claim that a naturally evolved virus escaped from a lab by mistake, some conspiracy theories have posited that SARS-CoV-2 was genetically engineered. In fact, researchers throughout the world, including in the US and China, have conducted research involving the creation of experimentally engineered hybrid coronaviruses. But there is no evidence that SARS-CoV-2 was genetically engineered, says Paraskevis, whose genomic analysis of the new virus was reported as a preprint in January.

I’m not saying this has been genetically engineered to be a bioweapon that’s escaped from the lab. . . . I’m just saying that [China is] collecting dangerous pathogens, [and] they have a history of letting them escape from the lab. —Steven Mosher, Population Research Institute

RNA viruses, which include coronaviruses, “accumulate mutations at a rate one million times faster than human DNA [does]. . . . It gives them the ability to survive against an immune response,” Paraskevis says. While the new coronavirus does have some genetic differences to other known viruses due to mutations, “there’s no evidence that this is the result of a human experiment,” he says, adding that if the virus were engineered, scientists would expect to see additional genetic material in its genome. For example, an early bioRxiv preprint on SARS-CoV-2 found HIV-like genetic sequences, but online commenters pointed out that “the findings were at most a coincidence” and that research has since been retracted, reports STAT.

As there are still many unknowns about SARS-CoV-2, researchers worldwide are trying to uncover as much as they can about the virus. Chinese researchers “released the genomic sequence incredibly rapidly online. . . . They were very public in sharing the most important first piece of information” about it, McCray tells The Scientist. “The fact that scientists all over the world had access to that genomic sequence” made a lot of early research possible, he says.

Emily Makowski is a freelance writer based in Boston. Find her on Twitter @EmilyRMakowski.