One of the great mysteries of the Covid-19 pandemic is how, exactly, the SARS-CoV-2 virus made the leap from wildlife into humans. Scientists who’ve analyzed the virus’s genome believe it came from a bat, likely in China. But Chinese epidemiologists have revealed little about how or where the first patients were infected.

One focus has been a wet market in Wuhan, where live wildlife was sold for food, because 66 percent of the first cluster of 41 cases in December 2019 had exposure to this market. Yet there is also genomic evidence and reports the virus could have been circulating earlier, in November. Which means there are many other possible places it could have jumped from a bat, or an intermediary species, to humans.

Finding the index case, or “patient zero,” for an infectious disease that’s just emerged can take months or years, if the person can even be found at all. So it’s not unusual we still don’t have one, especially for a disease with so much asymptomatic transmission.

Into the vacuum has seeped a potent, speculative, and confusing discussion about the virus’s origin, particularly in the US, where the GOP is intensifying its efforts to blame China for the pandemic.

In March, I offered explanations from virus experts for why they dismiss two of the theories that have surfaced about the coronavirus origin: that Chinese scientists bioengineered it in a lab and/or deployed it as a bioweapon.

In this piece, I’ll address the theory du jour: that a Chinese researcher was infected with the new virus inside a high-containment Wuhan laboratory and accidentally spread it, after which China attempted to cover it up.

This hypothesis has been circulating in US, UK, and Chinese media since February, with fresh reporting and speculation this month in the Daily Mail, Vanity Fair, Fox News, and the Washington Post. A Tuesday op-ed drawing solely from circumstantial evidence by chief “labber” Sen. Tom Cotton (R-AR) in the Wall Street Journal raised the question anew.

Riding the wave of these reports, President Donald Trump is also now using this potential avenue for blaming China; on April 15, he said his government was looking into whether the virus came from the Wuhan lab. Secretary of State Mike Pompeo has also said Beijing “needs to come clean” on what it knows about the virus’s origin.

Trump and the GOP’s motivation to establish new ways to blame China for the pandemic is clear: The president’s response to the pandemic has been abominable, and he faces an election in six months, with more than 22 million people unemployed and an economy heading toward recession. The lab-escape theory joins a variety of arguments he and his supporters are using — including scapegoating the World Health Organization and former President Barack Obama — to divert attention from his failures.

The Wuhan lab may also be the most tantalizing of the diversions, not just for Trump’s supporters but also for some political journalists and China hawks. What if the catastrophe is a result not of nature but of China’s incompetence with handling viruses and habit for suppressing information?

Such a spy-novel-worthy plot may seem plausible for a number of reasons: the Chinese government’s poor record of transparency; the fact that the Wuhan Institute of Virology, a research center with facilities in the same city where the virus first appeared, was studying dangerous pathogens, including bat coronaviruses; and US officials’ concerns about the lab’s safety standards in 2018, per the Washington Post.

Yet five scientists I interviewed, some of whom have worked extensively in China with researchers at the Wuhan Institute of Virology, say the pandemic can’t logically be pinned on an accident at that lab. (Researchers at the institute didn’t respond to my request for comment.)

The scientists I did speak to all acknowledge it’s not possible to definitively rule out the lab-escape theory. “The trouble with hypotheses is that they are not disprovable. You cannot prove a negative,” said Peter Daszak, president of EcoHealth Alliance and a disease ecologist who has studied emerging infectious diseases with colleagues in China. Yet he also sees the lab-escape theory as “ironic and preposterous.”

The scientists I spoke to also noted that all countries with high-level containment facilities, including China and the US, must be vigilant to prevent accidental leaks of dangerous diseases from labs. “I think we all are concerned about the increasing presence of high-consequence pathogens in laboratories and the issue of inadequate biosecurity,” said Dennis Carroll, the former director of USAID’s emerging threats division who helped design Predict, a surveillance program for dangerous animal viruses that the Trump administration chose to shut down in October. “We’ve seen examples of inadvertent release in the past and I’m sure we will see it in the future. So it’s a very major concern that we need to pay attention to.”

But scientists told me that based on what they know about the Wuhan Institute of Virology and the likelihood of a natural spillover event, they didn’t see lab escape as probable. And one expert added that it could be dangerous to get too preoccupied with this theory when the threat of another disease with pandemic potential from wildlife is so high.

Since politics will continue to propel this theory into the public sphere, let’s walk through six reasons a lab leak is unlikely.

1) The probability of the virus jumping from animals to humans outside the lab is much higher than the virus infecting humans inside the lab

Daszak is a scientist who has spent the past 15 years collaborating with scientists in China and other emerging disease hot spots around the world to find out where dangerous viruses lurking in wildlife — like the first SARS virus, MERS, and Ebola — are, how they get into people, and how to stop people from spreading them and spiraling into pandemics.

He says he’s confident SARS-CoV-2, the new coronavirus, originated in bats and jumped into people somewhere, likely in China, because he and his colleagues have established that viruses like it are out there and there are so many opportunities for this to happen.

“If you do the math on this, it’s very straightforward. ... We have hundreds of millions of bats in Southeast Asia and about 10 percent of bats in some colonies have viruses at any one time. So that’s hundreds of thousands of bats every night with viruses,” Daszak says. “We also find tens of thousands of people in the wildlife trade, hunting and killing wildlife in China and Southeast Asia, and millions of people living in rural populations in Southeast Asia near bat caves.”

Next, he says, consider the data he’s collected on people near bat caves getting exposed to viruses: “We went out and surveyed a population in Yunnan, China — we’d been to bat caves and found viruses that we thought could be high risk. So we sample people nearby, and 3 percent had antibodies to those viruses,” he says. “So between the last two and three years, those people were exposed to bat coronaviruses. If you extrapolate that population across the whole of Southeast Asia, it’s 1 million to 7 million people a year getting infected by bat viruses.”

Compare that, he says, to what we know about the labs: “If you look at the labs in Southeast Asia that have any coronaviruses in culture, there are probably two or three and they’re in high security. The Wuhan Institute of Virology does have a small number of bat coronaviruses in culture. But they’re not [the new coronavirus], SARS-CoV-2. There are probably half a dozen people that do work in those labs. So let’s compare 1 million to 7 million people a year to half a dozen people; it’s just not logical.”

But he told me he gets why people in the US, who aren’t regularly exposed to bats, have a hard time understanding how great the risk is of humans getting infected with novel coronaviruses circulating in bats.

“I understand — it’s a weird thing. Bats live out there, we don’t see them that often, we don’t realize how common, how abundant, how diverse they are,” he says. “In Southeast Asia, they carry their own viruses, and there’s just this really big interface between bats and people, every night, every day. People live in caves, people shelter from the rain in caves, people hunt bats.”

Angela Rasmussen, a virologist at Columbia University, also sees the lab-leak theory as very unlikely. “This virus came from bats under unknown circumstances,” she told me. “While I cannot rule out the lab-accident theory, there are so many other possibilities for how it could have happened. It could have been someone collecting bat guano for fertilizer, somebody cleaning out a barn, somebody exploring a cave. It could be any situation like that of someone in contact with animals who then spread it to other humans. There are so many other options than a lab leak.”

2) Yes, the Wuhan lab studied bat coronaviruses and SARS-related viruses. But there’s no evidence it discovered or was working on the new virus.

One of the big arguments “labber” theorists make for why we should suspect the Wuhan Institute of Virology of accidentally leaking the virus: Researchers there were already studying bat coronaviruses.

This is true; they published studies on the first SARS coronavirus that infected humans in 2003 and other bat coronaviruses, noting presciently in one paper, “it is highly likely that future SARS- or MERS-like coronavirus outbreaks will originate from bats, and there is an increased probability that this will occur in China.”

In 2020, they reported on a virus called RaTG13 that they’d discovered in a cave in Yunnan, China, in 2013. This virus shares 96 percent of its genome with the new coronavirus, which makes it the new virus’s closest known relative.

Some have speculated that perhaps the new coronavirus is derived from RaTG13. Yet virologists say it’s very unlikely: A 4 percent difference in genome is actually huge in evolutionary terms.

“The level of genome sequence divergence between SARS-CoV-2 and RaTG13 is equivalent to an average of 50 years (and at least 20 years) of evolutionary change,” said Edward Holmes, a professor at the University of Sydney who has published six academic papers this year on the genome and origin of SARS-CoV-2, in a statement. “Hence, SARS-CoV-2 was not derived from RaTG13.”

Another questionable assumption is that the mere existence of a related virus in the lab signals the possibility that SARS-CoV-2 was also there.

Daszak, who collaborates with the Wuhan bat coronavirus researchers and has co-authored papers with them, says this is false. He and the researchers there were indeed looking for viruses related to the first SARS virus, also known as SARS-1, in the hope of finding ones that might be a threat to humans. He confirmed that they had collected samples of bat feces that contained viruses and brought them back to the Wuhan lab.

However, he said, the new coronavirus is only 80 percent similar to SARS-1 — again, a very big difference. “No one [in Wuhan] cultured viruses from those samples that were 20 percent different, i.e., no one had SARS-CoV-2 in culture. All of the hypotheses [of lab release] depend on them having it in culture or bats in a lab. No one’s got bats in a lab, it’s absolutely unnecessary and very difficult to do.” (Cell culture is a way of storing viruses in vitro in a lab so they can be studied over long periods.)

3) Scientists like to gossip about new viruses. There was no chatter before the outbreak about the virus that causes Covid-19.

Carroll, the former director of USAID’s emerging threats division who also spent years working with emerging infectious disease scientists in China, agrees that there’s no evidence the Chinese researchers were working with a novel pathogen. His reasoning? He would have heard about it.

“The reason I’m not putting a lot of weight on [the lab-escape theory] is there was no chatter prior to the emergence of this virus to a discovery that would have ended up bringing the virus into a lab,” he says. “And if nothing else, the scientific community tends to be very gossipy. If there is a novel, potentially dangerous virus which has been identified, circulating in nature, and it’s brought into a laboratory, there is chatter about that. And when you look back retrospectively, there’s no chatter whatsoever about the discovery of a new virus.”

“If nothing else, the scientific community tends to be very gossipy”

Carroll is confident he would have heard about it because, in his current role as head of the Global Virome Project, he has his ear to the ground and remains active in the community.

When I asked if the Chinese researchers would have kept it secret, he replied, “People will come back and say China is China, they would have suppressed that information. But Chinese scientists, I think, are just as gregarious as everyone else.”

Rasmussen, for her part, also thinks there’s no suggestion of a cover-up. “I haven’t seen evidence of a grand conspiracy to cover up that there was a lab leak of this virus,” she said.

4) The US military chief reviewed the evidence and says “the weight of evidence seems to indicate natural” origin

As the lab-escape theory has gotten more attention in the media, we’ve learned that US military and intelligence officials have also been reviewing the possibility.

On April 14, we got a window into what those ongoing investigations have revealed so far about whether the virus leaked from a lab or jumped to people outside a lab, in nature.

“There’s a lot of rumor and speculation in a wide variety of media, blog sites, etc,” Chairman of the Joint Chiefs of Staff Gen. Mark Milley told reporters at the Pentagon. “It should be no surprise to you that we’ve taken a keen interest in that, and we’ve had a lot of intelligence look at that. And I would just say at this point, it’s inconclusive, although the weight of evidence seems to indicate natural [origin]. But we don’t know for certain.”

Brig. Gen. Paul Friedrichs, the Joint Staff surgeon, has also said “there is nothing to” the idea that the virus originated in a laboratory as a bioweapon experiment.

What’s more, as the New York Times reported in its sweeping April 11 review of the administration’s failed coronavirus response, intelligence officials couldn’t find evidence for the lab theory after Matthew Pottinger, the deputy national security adviser who was one of the earliest advocates for Trump to refer to Covid-19 as the “Wuhan virus,” pushed them to look for it:

With his skeptical — some might even say conspiratorial — view of China’s ruling Communist Party, Mr. Pottinger initially suspected that President Xi Jinping’s government was keeping a dark secret: that the virus may have originated in one of the laboratories in Wuhan studying deadly pathogens. In his view, it might have even been a deadly accident unleashed on an unsuspecting Chinese population. During meetings and telephone calls, Mr. Pottinger asked intelligence agencies — including officers at the C.I.A. working on Asia and on weapons of mass destruction — to search for evidence that might bolster his theory. They didn’t have any evidence. Intelligence agencies did not detect any alarm inside the Chinese government that analysts presumed would accompany the accidental leak of a deadly virus from a government laboratory.

Newsweek reported April 27 that in March the US Defense Intelligence Agency issued a report that “reveals that U.S. intelligence revised its January assessment in which it ‘judged that the outbreak probably occurred naturally’ to now include the possibility that the new coronavirus emerged ‘accidentally’ due to ‘unsafe laboratory practices’ in the central Chinese city of Wuhan.”

Again, the US government’s investigation into the theory is ongoing, so it’s possible it will turn up new information. But so far, the reports we do have suggest the natural origin is more likely.

5) Wuhan Institute of Virology scientists deny a lab leak

There’s no question the Chinese government and ruling party made grave errors in managing the outbreak from the outset that contributed to its spread around the world. And according to Nature, the government is putting in place new rules in reviewing research on the virus origin.

As Sen. Ed Markey (D-MA) put it to my colleague Alex Ward, “We don’t know the true extent of the Chinese government’s complicity in the spread of the virus, and we may never have a full picture due to their obfuscation and control of information. We do know that they lied to their own people and the world about the details and spread of the virus, and today we face a pandemic that has left no country untouched.”

Related 12 experts on how the US should hold China accountable for the coronavirus

And China should, as the Washington Post’s David Ignatius pointed out on April 23, “promptly begin a serious, credible investigation into how the Covid-19 pandemic began.”

But the scientists I interviewed say that we still shouldn’t immediately conflate the work of the highly regarded Chinese scientists who work at the lab with the transgressions of their government.

We also have the word of one of the top virologists at the Wuhan lab, documented in news articles, that she too wondered if the virus could have originated in her lab and then took steps to verify it didn’t match any of the viruses they had in culture.

In this excellent article by Jane Qiu in Scientific American, we learned that the team at the Wuhan lab led by Shi Zhengli, known as China’s “bat woman” for her 16 years of work collecting samples of bat viruses in caves, sequenced the genome of the new virus in early January and published it on January 23:

Shi instructed her team to repeat the tests and, at the same time, sent the samples to another laboratory to sequence the full viral genomes. Meanwhile she frantically went through her own laboratory’s records from the past few years to check for any mishandling of experimental materials, especially during disposal. Shi breathed a sigh of relief when the results came back: none of the sequences matched those of the viruses her team had sampled from bat caves. “That really took a load off my mind,” she says. “I had not slept a wink for days.”

Yuan Zhiming, vice director of the Wuhan Institute of Virology, also recently spoke up on Chinese state broadcaster CGTN. “As people who carry out viral study, we clearly know what kind of research is going on in the institute and how the institute manages viruses and samples. As we said early on, there is no way this virus came from us,” he said, according to NBC News.

I asked Jim LeDuc, head of the Galveston National Laboratory, a level-4 biosafety lab in Texas, for his thoughts on Yuan’s statement. “I like to think that we can take Zhiming Yuan at his word, but he works in a very different culture with pressures we may not fully appreciate,” he said. In other words, we don’t know what kind of pressures he might be under from his government to make such a statement.

LeDuc says the hypothesis that the animal market played a role in the virus jumping to humans also remains strong. “The linkage back to the market is pretty realistic, and consistent with what we saw with SARS,” said LeDuc. “It’s a perfectly plausible and logical explanation: The virus exists in nature and, jumping hosts, finds that it likes humans just fine, thank you.“

6) State Department officials worried about safety issues at the Wuhan lab in 2018. This is concerning but doesn’t prove its scientists were incompetent.

In an April 14 piece, Josh Rogin, a global opinions columnist for the Washington Post, reported that in January 2018, the US Embassy in Beijing dispatched science diplomats to the Wuhan Institute of Virology who later sent back cables that warned of “safety and management weaknesses at the WIV lab and proposed more attention and help.”

Rogin went on to cite an anonymous senior administration official’s belief that “the cables provide one more piece of evidence to support the possibility that the pandemic is the result of a lab accident in Wuhan.”

The article sparked a rich discussion on Twitter, with Rasmussen of Columbia pointing out, “The bottom line is that those vague diplomatic cables do not provide any specific information suggesting that #SARSCoV2 emerged from incompetence or poor biosafety protocols or anything else.”

I had a great exchange with @JeremyKonyndyk about the state department cables reported yesterday by @joshrogin and the credence they supposedly lend to the "lab accident" origin story of #SARSCoV2. Jeremy distilled this into the perfect meme: https://t.co/2CiWvbtt8l — Dr. Angela Rasmussen (@angie_rasmussen) April 15, 2020

In a follow-up conversation with me, she reiterated: “This line that they’re incompetent, it doesn’t hold water with me.”

Other scientists who have worked with the Wuhan Institute of Virology have spoken up about its standards and practices in the face of the theory it leaked the virus.

“I have worked in this exact laboratory at various times for the past 2 years,” wrote Danielle Anderson, scientific director of the Duke-NUS Medical School ABSL3 Laboratory, in a March 2 post on Health Feedback, a site where scientists review the veracity of news reports. “I can personally attest to the strict control and containment measures implemented while working there. The staff at WIV are incredibly competent, hardworking, and are excellent scientists with superb track records.”

Gerald Keusch, a professor of medicine and international health and associate director of Boston University’s National Emerging Infectious Diseases Laboratories, also doubts the lab would have been prone to accidents.

“The Wuhan lab is (as far as I know because I have never visited) state of the art in terms of safety and security systems and protocols, and because [the Galveston National Laboratory in the US] helped to train many of them and has collaborations I would bet they are highly professional, which makes the likelihood of an accident remote,” he said. “Is it possible? Yes. Is it likely? In my opinion, no.”

We may never find out exactly when this virus made the leap into humans. But focusing too much on the lab-leak theory could ultimately be dangerous.

Since there’s no robust evidence in support of the lab-leak theory, Daszak says he’s worried that it could become a conspiratorial distraction with serious consequences.

“There is a group of people who do not want to believe that this is a natural, unfortunate incident,” he said. “And the real bad part of that is that if we don’t believe that we won’t try and stop other viruses in wildlife. Instead, we will focus on labs and close them down when they’re the ones trying to develop vaccines to cure us right now. I mean, how ironic could we go?”

Carroll says the lab-leak theory, even if there isn’t evidence to support it, is a healthy reminder that lab accidents can happen and that biosecurity needs attention in country studying dangerous pathogens. But he’s also much more concerned with preventing the next pandemic.

Pandemics, says Carroll, do not have to happen. “They are a consequence of the way we live. You can pick [viruses] up earlier if you’re really including in your surveillance those places where animals and people are having high-risk interaction, those hot spots.”

If you have that surveillance, “you would never get a virus sweeping out of hand. You would never get a repeat of an uncontrolled, unrecognized event.”

Which means it’s time for the whole world to invest in studying the viruses in the bat caves and beyond, and building up the systems to stop them from spreading in humans, so this doesn’t happen again. Because otherwise, it will.

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