It's unlikely that SARS-CoV-2 escaped from a laboratory so don't jump to conclusions just because of calls to investigate the possibility, NCSE Executive Director Ann Reid writes in response to the growing calls for an investigation into the origins of the novel coronavirus.
Photo by Heather Barnes on Unsplash.
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Here’s a scenario for you:
You are the manager of a large hotel with hundreds of guests. One morning you enter the kitchen and discover that someone has eaten a big slice of the lavish wedding cake you had baked for a reception that day. What is the most likely explanation? One of your guests snuck down in the night and perpetrated the crime? One of your guests suffered from an undiagnosed case of somnambulism (sleepwalking) and unknowingly ate the cake? Or aliens from outer space came into the hotel, ate some cake, and departed without leaving a trace?
I think you’ll agree that the first scenario is the most likely one. Most of us will reject the aliens-from-space hypothesis out of hand, but we can’t as easily rule out the sleepwalking scenario. If a suspect can be found and convinced to confess, our work is over. But if not, and it’s truly critical to find the true answer (like, say, we’re not talking about a stolen piece of cake but rather a murder victim in the hotel’s walk-in refrigerator), you could investigate. Somnambulism is real, if rare, and people don’t always remember what they did while sleepwalking. Security cameras, card-key time stamps, fingerprints, DNA analysis — any of these could be pressed into service to find an answer. True, you might never figure out what exactly happened, but you’d be irresponsible not to check out all the possibilities.
I hope you won’t find the comparison flippant, but this is sort of what’s happening with efforts to further investigate the origin of SARS-CoV-2, the virus that causes COVID-19. We’ve written about this before. In fact, in just our second article about the science related to the pandemic, way back in March 2020, we discussed whether we knew enough to be sure that pangolins were the intermediary between bats and humans (spoiler: we did not). More recently, when conspiracy theories suggesting that the virus had been deliberately engineered and released were circulating widely, we discussed the reasons that scientists roundly rejected that possibility.
But now pressure is rising to investigate the possibility that the virus accidentally escaped from a research laboratory, specifically a laboratory that was studying bat viruses in Wuhan, China, where the pandemic was first detected. (Do I need to point out that there is absolutely no excuse for harassing Chinese nationals, much less Asian Americans, because this virus originated in China?) Clearly it’s not only of academic interest to determine the origin of a coronavirus that continues to sicken and kill millions of people around the world. Understanding how animal viruses move from their natural reservoirs into humans is crucial for putting in place the monitoring and preventative measures that will make future pandemics less likely; if wild viruses being studied in laboratories can make this leap, as the accidental-escape theory suggests, we need to know about it.
Most scientists still agree that the overwhelmingly more likely scenario is that the virus emerged from a natural reservoir, probably into an intermediate species before infecting humans.
Most scientists still agree that the overwhelmingly more likely scenario is that the virus emerged from a natural reservoir, probably into an intermediate species before infecting humans. Proving this, however, is going to be exceptionally challenging. Identifying the intermediate host is hard, especially given that we don’t know exactly when or where the crossover happened. It seems very likely that SARS-CoV-2 originated in wild bats — it is about 96% identical to the most closely related wild bat virus. That seems pretty close, but in a virus with 30,000 nucleotides in its genome, that means there are about 1,200 nucleotides that differ. Where did those changes accumulate and how long did it take? Is the virus still circulating in an intermediate host? If we don’t find an intermediate host, at what point can we say that we’ve exhaustively sampled all possible intermediaries and therefore we can rule out natural zoonotic transmission? It took about two years to track down the presumed path by which the first SARS virus emerged (from bats through palm civets). The pathway for other emergent viruses—notably Ebola—have never been definitively identified, despite years of effort. If the intermediate host for SARS-CoV-2, or an even more closely related bat virus, is found, the puzzle is solved. But not finding an intermediate host doesn’t mean it’s not there.
Meanwhile, even though the overwhelming likelihood remains that SARS-CoV-2 evolved naturally, the accidental-escape theory hasn’t been ruled out. Still, there are a lot of reasons why that scenario is unlikely. Foremost among them, to my mind, is that it’s hard to imagine how a wild bat virus could evolve the ability to be both infectious to humans and transmissible between humans in a highly controlled laboratory environment, even admitting the possibility of occasional safety lapses (which have so far only been rumored, not proven). Remember, the most closely related bat virus — which cannot infect humans — differs at over 1,200 nucleotides. Nevertheless, making a good-faith effort to rule out that possibility is important, and that is why a group of prominent scientists recently called for a new investigation, suggesting that an earlier one was not as thorough as it should have been.
Assuming that international authorities can come to an agreement on what would constitute a thorough investigation, and the scientists in the Wuhan laboratory are able to cooperate with that investigation (neither of which are inevitable, to be sure), the result will be a report with either of two possible conclusions. The most likely conclusion is that there is no evidence that any virus resembling SARS-CoV-2 was present in the laboratory and therefore SARS-CoV-2 is extremely unlikely to have escaped from there. The much less likely conclusion is that a virus very similar to SARS-CoV-2 (and I mean Very Similar — that is, much more closely related to SARS-CoV-2 than any wild bat viruses the lab might have been studying) was present and safety protocols were breached. The report probably won’t say the latter scenario is absolutely impossible. Science rarely deals in that level of certainty. So any future report is more likely to conclude that a laboratory escape is vanishingly unlikely and therefore that the virus probably emerged naturally from a wild source, even if we never find that source.
Some people will not be satisfied. Indeed, they will continue to believe the deliberate bioweapon scenario — the viral equivalent of aliens breaking into the hotel and stealing the cake. We’d all like a definitive answer; we’re unlikely to get one. But it’s worth having some patience while an unlikely but not impossible scenario is investigated.
