Two studies published in Science offer a more complete look at the origins of Covid-19. An international team of researchers has determined that at least two coronavirus variants were transmitted from live animals to humans at the Huanan Seafood Wholesale Market in Wuhan, China.
Dr. Joel O. Wertheim is an associate professor in the Division of Infectious Diseases and Global Public Health at the UC San Diego School of Medicine, and a co-author on both papers.
“It’s vital that we know as much about the origin of Covid-19 as possible because only by understanding how pandemics get started can we hope to prevent them in the future,” said Dr. Wertheim.
“I think there’s been consensus that this virus did in fact come from the Huanan Market, but a strong case for multiple introductions hasn’t been made by anyone else yet.”
Based on genetic research, the researchers determined that there were two animal-to-human jumps with two different virus strains. The first jump occurred in late November 2019, while the second lineage jumped within weeks of the first. This means that multiple zoonotic transmission events likely led to the COVID-19 pandemic.
This research is consistent with another recently published study conducted by the Chinese Center for Disease Control and Prevention.
“We felt validated, but what we felt more was immense pressure because they beat our preprint to the punch by about 12 hours, and we could only discuss their findings in light of ours,” said Dr. Wertheim.
The researchers are cautiously confident about their conclusions. “While I’m hesitant to call it proof, what we presented is the most comprehensive explanation for the SARS-CoV-2 genomic diversity at the outset of the pandemic,” said Dr. Wertheim. “There are really no other good explanations for both of these strains being at the market except for multiple jumps into humans.”
Study lead author Jonathan E. Pekar said that the evolution and spread of the virus were inevitable, considering the circumstances.
“Everything complicated happened before that introduction,” explained Pekar. “The last step is just extended contact and transmission from hosts to humans. At that point, it would actually be unusual to only have one introduction. We’ve seen this before with MERS-CoV (a similar zoonotic virus). We’ve seen it with humans giving SARS-CoV-2 to minks on farms and then minks giving it back to humans.”
“This has happened before, and it’s going to keep happening. Nature is a better lab than humans will ever be.”