In early 2020, Kristian Andersen wrote to Anthony Fauci about the possibility of an engineered coronavirus. His research has since dispelled those suspicions.Among the thousands of pages of Dr. Anthony S. Fauci’s emails obtained recently by The Washington Post and BuzzFeed News, a short note from Kristian Andersen, a virologist at the Scripps Research Institute in La Jolla, Calif., has garnered a lot of attention.Over the past year, Dr. Andersen has been one of the most outspoken proponents of the theory that the coronavirus originated from a natural spillover from an animal to humans outside of a lab. But in the email to Dr. Fauci in January 2020, Dr. Andersen hadn’t yet come to that conclusion. He told Dr. Fauci, the government’s top infectious disease expert, that some features of the virus made him wonder whether it had been engineered, and noted that he and his colleagues were planning to investigate further by analyzing the virus’s genome.The researchers published those results in a paper in the scientific journal Nature Medicine on March 17, 2020, concluding that a laboratory origin was very unlikely. Dr. Andersen has reiterated this point of view in interviews and on Twitter over the past year, putting him at the center of the continuing controversy over whether the virus could have leaked from a Chinese lab.When his early email to Dr. Fauci was released, the media storm around Dr. Andersen intensified, and he deactivated his Twitter account. He answered written questions from The New York Times about the email and the fracas. The exchange has been lightly edited for length.Much has been made of your email to Dr. Fauci in late January 2020, shortly after the coronavirus genome was first sequenced. You said, “The unusual features of the virus make up a really small part of the genome (

Researchers urge an open mind, saying lack of evidence leaves theories of natural spillover and laboratory leak both viable.A group of 18 scientists stated Thursday in a letter published in the journal Science that there is not enough evidence to decide whether a natural origin or an accidental laboratory leak caused the Covid-19 pandemic.They argued, as the U.S. government and other countries have, for a new investigation to explore where the virus came from.The organizers of the letter, Jesse Bloom, who studies the evolution of viruses at the Fred Hutchinson Cancer Research Center in Seattle, and David Relman, a microbiologist at Stanford University, said they strove to articulate a wait-and-see viewpoint that they believe is shared by many scientists. Many of the signers have not spoken out before.“Most of the discussion you hear about SARS-CoV-2 origins at this point is coming from, I think, the relatively small number of people who feel very certain about their views,” Dr. Bloom said.He added: “Anybody who’s making statements with a high level of certainty about this is just outstripping what’s possible to do with the available evidence.”The new letter stated: “Theories of accidental release from a lab and zoonotic spillover both remain viable.”Proponents of the idea that the virus may have leaked from a lab, especially the Wuhan Institute of Virology in China where SARS viruses were studied, have been active this year since a World Health Organization team issued a report claiming that such a leak was extremely unlikely, even though the mission never investigated any Chinese labs. The team did visit the Wuhan lab, but did not investigate it. A lab investigation was never part of their mandate. The report, produced in a mission with Chinese scientists, drew extensive criticism from the U.S. government and others that the Chinese government had not cooperated fully and had limited the international scientists’ access to information.The new letter argued for a new and more rigorous investigation of virus origins that would involve a broader range of experts and safeguard against conflicts of interest.The call for further investigation echoed statements urging further inquiry by the Biden administration and other nations, as well as by the director of the W.H.O., Dr. Tedros Adhanom Ghebreyesus.World Health Organization investigators arriving at the Wuhan Institute of Virology in February. The letter challenged the team’s conclusion that a natural origin of the leap from animals to humans was most likely.Hector Retamal/Agence France-Presse — Getty ImagesUnlike other recent statements, the new letter did not come down in favor of one scenario or another. Recent letters by another group of scientists and international affairs experts argued at length for the relative likelihood of a laboratory leak. Previous statements from other scientists and the W.H.O. report both asserted that a natural origin was by far the most plausible.Michael Worobey, an evolutionary biologist at the University of Arizona, said he signed the new letter because “the recent W.H.O. report on the origins of the virus, and its discussion, spurred several of us to get in touch with each other and talk about our shared desire for dispassionate investigation of the origins of the virus.”“I certainly respect the opinion of others who may disagree with what we’ve said in the letter, but I felt I had no choice but to put my concerns out there,” he said.Another signer, Sarah E. Cobey, an epidemiologist and evolutionary biologist at the University of Chicago, said, “I think it is more likely than not that SARS-CoV-2 emerged from an animal reservoir rather than a lab.”But “lab accidents do happen and can have disastrous consequences,” she added. “I am concerned about the short- and long-term consequences of failing to evaluate the possibility of laboratory escape in a rigorous way. It would be a troublesome precedent.”The list of signers includes researchers with deep knowledge of the SARS family of viruses, such as Ralph Baric at the University of North Carolina, who had collaborated with the Chinese virologist Shi Zhengli in research done at the university on the original SARS virus. Dr. Baric did not respond to attempts to reach him by email and telephone.While this group of scientists does not single out any researchers by name, the letter finds fault with those who have also been vocal in supporting the theory of a natural origin, citing a lack of evidence.Kristian Andersen, a virologist at the Scripps Research Institute in La Jolla, Calif., has been a strong proponent of the overwhelming likelihood of a natural origin. He was one of the authors of an often cited paper in March 2020 that dismissed the likelihood of a laboratory origin based largely on the genome of the SARS-CoV-2 virus that causes Covid-19. “We do not believe any type of laboratory-based scenario is plausible,” that paper stated.Speaking for himself only, Dr. Relman said in an interview that “the piece that Kristian Anderson and four others wrote last March in my view simply fails to provide evidence to support their conclusions.”Dr. Andersen, who reviewed the letter in Science, said that both explanations were theoretically possible. But, “the letter suggests a false equivalence between the lab escape and natural origin scenarios,” he said. “To this day, no credible evidence has been presented to support the lab leak hypothesis, which remains grounded in speculation.”Instead, he said, available data “are consistent with a natural emergence of a novel virus from a zoonotic reservoir, as has been observed so many times in the past.” He said he supported further inquiry into the origin of the virus.Angela Rasmussen, a virologist at University of Saskatchewan’s Vaccine and Infectious Disease Organization, has criticized the politicization of the laboratory leak theory.She supports further investigation, but said that “there is more evidence (both genomic and historical precedent) that this was the result of zoonotic emergence rather than a laboratory accident.”