But those market viruses actually have three extra mutations that are missing from SARS-CoV-2 samples collected weeks later. In other words, those later viruses look more like coronaviruses found in bats, supporting the idea that there was some early lineage of the virus that did not pass through the seafood market.
Dr. Bloom found that the deleted sequences he recovered from the cloud also lack those extra mutations. “They’re three steps more similar to the bat coronaviruses than the viruses from the Huanan fish market,” Dr. Bloom said.
This suggests, he said, that by the time SARS-CoV-2 reached the market, it had been circulating for awhile in Wuhan or beyond. The market viruses, he argued, aren’t representative of full diversity of coronaviruses already loose in late 2019.
“Maybe our picture of what was present early in Wuhan from what has been sequenced might be somewhat biased,” he said.
In his report, Dr. Bloom acknowledged that this conclusion would have to be confirmed with a deeper analysis of the virus sequences. Dr. Worobey said that he and his colleagues are working on a large-scale study of SARS-CoV-2 genes to better understand its origin and that they’ll now add Dr. Bloom’s 13 recovered sequences.