Among the thousands of pages of email from Dr. Anthony S. Fauci, recently published by BuzzFeed News, got a lot of attention from a brief note from Kristian Andersen, a virologist at the Scripps Research Institute in La Jolla, California.

Last year, Dr. Andersen one of the staunchest proponents of the theory that the coronavirus came from a natural overflow from an animal to humans outside of a laboratory. But in the email to Dr. Fauci in January 2020 was Dr. Andersen has not yet reached this conclusion. He said Dr. Fauci, the government’s leading infectious disease expert, said he wondered if some characteristics of the virus had been tampered with, and noted that he and his colleagues planned to further study the virus’s genome.

The researchers published these results in an article in the journal Nature Medicine on March 17, 2020, and concluded that laboratory provenance was very unlikely. Dr. Andersen reiterated this point of view in interviews and on Twitter over the past year, placing it at the center of the ongoing controversy over whether the virus might have leaked from a Chinese laboratory.

When his early email to Dr. Fauci was released, the media storm intensified around Dr. Andersen and he deactivated his Twitter account. He answered written questions from the New York Times about the email and the dispute. The exchange was easily edited for the length.

At that time, based on limited data and preliminary analysis, we observed traits that appeared to be potentially unique to SARS-CoV-2. We had not seen these traits in other related viruses from natural sources, so we investigated whether they had been incorporated into the virus.

These features included a structure known as the furin cleavage site, which enables the SARS-CoV-2 spike protein to be cleaved by furin, an enzyme found in human cells, and another structure known as the receptor binding domain and which enabled the virus to anchor to the outside of human cells through a cell surface protein called ACE2.

Recognition…Scripps Research Institute

This was an indication of the characteristics of SARS-CoV-2 that we identified based on early analysis that did not appear to have an obvious immediate evolutionary precursor. We had not yet carried out any more in-depth analyzes to arrive at a result, but shared our preliminary observations.

I warned in the same email that we needed to look at the question much more closely, and that new data and analysis could change our opinions in a matter of days – which they did.

The traits in SARS-CoV-2 that initially suggested possible engineering were identified in related coronaviruses, meaning traits that initially looked unusual to us weren’t.

Many of these analyzes were completed within a few days while we were working around the clock, which allowed us to reject our preliminary hypothesis that SARS-CoV-2 might have been engineered while other “laboratory” -based scenarios were still on Test bench were table.

Even more extensive analysis, significant additional data, and in-depth research to broadly compare genomic diversity between coronaviruses led to the peer-reviewed study published in Nature Medicine. For example, we looked at data from coronaviruses found in other species such as bats and pangolins, which showed that the traits that originally appeared unique to SARS-CoV-2 were in fact found in other related viruses.

Overall, this is a textbook example of the scientific method, where a tentative hypothesis is rejected in favor of a competing hypothesis after more data is available and analysis is complete.

Furin cleavage sites are found throughout the coronavirus family, including the beta coronavirus genus to which SARS-CoV-2 belongs. There has been much speculation that patterns found in the virus’s RNA responsible for certain parts of the furin cleavage site provide evidence of the technique. Specifically, people point to two “CGG” sequences that code for the amino acid arginine in the furin cleavage site as strong evidence that the virus was made in the laboratory. Such statements are factually incorrect.

While it’s true that CGG is less common than other patterns that code for arginine, the CGG codon is found elsewhere in the SARS-CoV-2 genome and in the genetic sequence[s] that contain the CGG codon found in SARS-CoV-2 are also found in other coronaviruses. These results, along with many of the other technical features of the website, strongly suggest that it evolved naturally and there is very little chance that it was developed by anyone.

As we noted in our article last March, it is currently impossible to prove or disprove specific hypotheses about the origin of SARS-CoV-2. While both laboratory and natural scenarios are possible, they are not equally likely – precedents, data, and other evidence advocate natural occurrence as the highly likely scientific theory for the occurrence of SARS-CoV-2, while the laboratory leak remains a speculative hypothesis based on guesswork.

Based on detailed analyzes of the virus so far carried out by researchers around the world, it is extremely unlikely that the virus has been tampered with. The scenario where the virus was found in nature, taken to the laboratory, and then accidentally released[d] is similarly unlikely according to current knowledge.

In contrast, the scientific theory about the natural development of SARS-CoV-2 presents a much simpler and more likely scenario. The occurrence of SARS-CoV-2 is very similar to that of SARS-CoV-1, including its seasonal timing Location and its connection to the human food chain.

My main concern last spring, which remains to this day, is to conduct research to find out exactly how SARS-CoV-2 originated in the human population.

I am not going to speak to what government officials and other scientists did or did not say or think. My comments and conclusions are based solely on scientific research, and I strongly believe that careful, well-supported public communication on complex issues is of paramount importance.

First of all, it’s important to say that the scientific community has made tremendous strides in understanding Covid-19 in a remarkably short period of time. Lively debate is an integral part of science, and that’s what we’ve seen regarding the origins of SARS-CoV-2.

I think it can be difficult at times for the public to watch the debate and see the likelihood of the various hypotheses. This is especially true where science is politicized and the current defamation of scientists and subject matter experts is setting a dangerous precedent. We saw that in the climate change debate and now we see it in the debate on various facets of the Covid-19 pandemic.

During this pandemic, I have done my best to explain what the scientific evidence is and suggest, and I have no regrets.

I have always supported further research into the origin of SARS-CoV-2, including President Biden’s recent appeal, as it is important that we better understand how the virus came about.

As with any scientific process, there are several things that would give credibility to the laboratory leak hypothesis that would make me change my mind. For example, any credible evidence that SARS-CoV-2 was in the Wuhan Institute of Virology before the pandemic – be it in a freezer, in tissue culture, or in animals, or epidemiological evidence of very early confirmed Covid-19 related cases with The Institute.

Other evidence could add further weight to the natural origin hypothesis. This includes the identification of an intermediate product [animal] host (if any). Now that we know that live animals have been sold in markets across Wuhan, a further understanding of the flow of animals and the associated supply lines could add additional credibility to natural emergence.

I’ve always seen Twitter as a way to interact with other scientists and the public to foster an open and transparent dialogue about science.

Increasingly, however, I found that information and comments I posted were taken out of context or misrepresented in order to spread false narratives, especially about the origins of SARS-CoV-2. Daily attacks on scientists and the scientific method have also become common, and many conversations have moved far from science.

For these reasons, I felt like I was no longer productive to contribute to the platform and decided that it would be more productive for me to invest more time in our research on infectious diseases, including that on Covid-19.