Science journalist Nicholas Wade recently argued that circumstantial evidence suggests the COVID-19 pandemic began with a lab leak at the Wuhan Institute of Virology. As I noted here yesterday, one of his biggest pieces of evidence is the virus's supposedly anomalous furin cleavage site—a specific protein that it uses to enter human cells.
Wade claims that "no known SARS-related beta-coronavirus, the class to which [the novel coronavirus] belongs, possesses a furin cleavage site." To back this up, Wade quotes the Nobel-winning biologist David Baltimore: "When I first saw the furin cleavage site in the viral sequence, with its arginine codons, I said to my wife it was the smoking gun for the origin of the virus. These features make a powerful challenge to the idea of a natural origin for" the COVID-19 virus, SARS-CoV-2.
As I earlier reported, some research supports this contention, while other research does not. Now the Scripps Research Institute immunologist Kristian Andersen has weighed in on the "does not" side. "The site is not a 'smoking gun', nor does it 'make a powerful challenge to the idea of a natural origin,'" he writes. Last year, I should note, Andersen and some colleagues published an article in Nature Medicine that concluded the coronavirus "is not a laboratory construct or a purposefully manipulated virus."
Without going too deeply into technical details, Andersen cites the same Stem Cell Research article to which I had linked as evidence that furin cleavage sites "are abundant, including being highly prevalent in coronaviruses. While SARS-CoV-2 is the first example of a SARSr virus with an FCS [furin cleavage site], other betacoronaviruses (the genus for SARS-CoV-2) have FCSs," including the Middle Eastern Respiratory Syndrome (MERS) virus and the Hong Kong University 1 (HKU1) virus. He adds, "There is nothing mysterious about having a 'first example' of a virus with an FCS."
While acknowledging that researchers don't know for sure how the virus acquired its furin cleavage site, Andersen then reviews four natural ways the COVID-19 virus could have done so. He concludes that "Baltimore's first point—that the FCS found in SARS-CoV-2 is somehow unusual—is simply incorrect. FCSs are found in a multitude of different coronaviruses."
Anderson moves on to Baltimore's claim that the codons associated with the FCS are anomalous. Codons are specific sequences of three consecutive nucleotides in the genetic code; they specify particular amino acids for constructing proteins. While somewhat rare, Andersen points out that all sorts of coronaviruses naturally contain the codons that Baltimore suggests is evidence of lab manipulation.
"So Baltimore's second point is also false," concludes Andersen. "Baltimore does not provide any evidence to support his hypothesis and the data support a natural origin."
That being said, Andersen adds this:
Does this disprove a lab leak? No. However, it disproves there being a "smoking gun" in the FCS and lends further evidence to natural emergence—but it also does not *prove* that scenario. To this day, we have yet to see any scientific evidence supporting a lab leak.
The lively scientific debate over the origins of the COVID-19 virus will surely continue. And suspicions about whether the virus escaped the Wuhan lab will surely remain as long as the Chinese government refuses to allow a thorough investigation and keeps acting like it has something to hide.