Medical Examiner

What’s Actually Changed With the Lab Leak Theory

We’re all talking about it now.

Security personnel stand guard outside the Wuhan Institute of Virology
Outside the Wuhan Institute of Virology in February as members of the World Health Organization (WHO) investigate the origins of the COVID-19 coronavirus. Hector Retamal/Getty Images

If you’ve only kind of been paying attention to the news, you would be forgiven for thinking that the consensus is shifting on whether SARS-CoV-2 escaped from a lab in Wuhan, China. Discussion of the “lab leak theory,” as it’s called, is everywhere: It’s on the letters page of the prestigious scientific journal, Science. It’s in long pieces by former New York Times journalists on smaller outlets, but it’s also in seemingly every major paper. It’s in Slate. It’s even on President Biden’s agenda—on Wednesday, he called on the intelligence community to investigate whether it could be true.

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But we’re not talking about the lab leak theory now because there’s direct evidence for it, or even much evidence for it at all. We are talking about it because there is an ongoing scientific inquiry into how the pandemic started, and because a number of journalists are following those lines of inquiry or see talking about it as a corrective to past bias. Simply: There is a very small possibility that the virus came from a lab, a possibility some scientists (and now many other people) are interested in exploring further. A recent New York Times headline might sum it up best: “Scientists Don’t Want to Ignore the ‘Lab Leak’ Theory, Despite No New Evidence.” Or, as Mike Ryan, executive director of the WHO Health Emergencies Programme, said Friday: “Over the last number of days, we have seen more and more discourse in the media, with terribly little actual little news, or evidence, or new material, and this is disturbing.” Or as Washington Post foreign affairs correspondent Emily Rauhala tweeted:

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What the spate of coverage has done is expand the sphere of people weighing in. Political analyst Nate Silver suggested that a lot of smart people believe the lab leak theory to be at least 50 percent likely, and asked people to reply with their own guesses. Because we’re talking about two possibilities, and there’s a lot of recent attention being paid to one, it can be kind of tempting to suspect that they are equally likely, or at least that the lab leak option is gaining some kind of meaningful ground in terms of evidence. But it’s not. Florian Krammer, a virologist at Mount Sinai, replied to Silver, the lab leak is “not impossible, but less than 1%,” adding that he put the chances “below that for an engineered virus.” The Facebook page Dear Pandemic, run by a team of experts, offers a simple explanation as to why that probability is so low—basically, viruses jump from animals to humans all the time, and therefore the idea that it leaked from a lab is an “extraordinary” claim, which, while possible, requires “extraordinary evidence” to deem likely.

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Now, this extraordinariness doesn’t mean that the possibility shouldn’t be considered. (Which, it is!) But it’s useful to note that even the scientists bringing attention to the lab leak theory—who suggest that the chances here might be a little higher—are saying that it’s just a possibility. “I want to be really clear that I still think wildlife trade is a plausible scenario,” Alina Chan, one of the theory’s main proponents, told Slate’s What Next in April. For a while, Chan was an outlier as an early proponent of the theory, but earlier this month, 18 scientists published a letter in Science arguing that it needed to be more thoroughly considered: “We must take hypotheses about both natural and laboratory spillovers seriously until we have sufficient data,” they wrote.* As David Relman, a microbiologist who signed the letter, told Amy Maxmen in Nature, “I am not saying I believe the virus came from a laboratory.” Another author on the letter, virologist Jesse Bloom, told the Times: “In the case of SARS-CoV-2 origins, I still am not confident about what happened.” He added that he was worried that if he didn’t say something, the consensus was going to close in on the virus coming from animals, despite there not being more definitive evidence as to how that happened, either.

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Absent new information the public should be vigilant about what various arguments regarding the lab leak hypothesis are trying to achieve. Are they pushing for a specific investigation? Are they asserting that having previously not spent more time and energy on this outside possibility was irresponsible? (It’s frankly hard to see how, in a climate where the president was referring to the “China virus” and “kung flu,” erring on the side of caution was the irresponsible path.) Or are they decrying prominent examples of forceful statements from a year ago that were against entertaining the idea of the virus coming from a lab? It feels to some extent like we are all, at best, sitting around marveling that a leak could be possible, and, at worst, hemming and hawing that someone should have been doing more about this earlier, but failed to.

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The simple fact is that the facts have not really changed. What’s changed is that there’s been a WHO investigation, which some scientists believe was insufficient. What’s also changed is that we’re in a slightly safer environment to ask questions about what remains the outside-chance explanation for the origin of the virus. And—given that the pandemic is slowing in the U.S.—scientists are in a better position to think about the implications of either explanation, even if we never find out what really happened. Which is to say: The lab leak hypothesis hasn’t suddenly become more likely. But it is in vogue.

Correction, June 1, 2021: This piece originally misspelled Alina Chan’s last name.

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