The Facts – and Gaps – on the Origin of the Coronavirus
A year and a half into the COVID-19 pandemic — and with a death toll approaching 4 million lives — how the coronavirus came to spark a global scourge remains unknown. Was it the result of a spillover from an animal to a human, as has happened repeatedly in the past? Or did the virus accidentally escape from a nearby lab?
The default answer for most scientists has been that the virus, SARS-CoV-2, probably made the jump to humans from bats, if it was a direct spillover — or, more likely, through one or more intermediate mammals. That’s what happened with the coronaviruses responsible for SARS and MERS, and such zoonotic events are standard fare for emerging pathogens.
But without identification of a near-identical virus in a bat or other animal, scientists cannot be completely certain. Stepping into that void is speculation that a naturally occurring or lab-manipulated virus may have inadvertently infected a researcher, who then spread it to others.
In recent months, consideration of the so-called lab leak hypothesis has seemingly gained momentum. In May, a group of 18 scientists wrote a letter in the journal Science criticizing the World Health Organization’s investigation into the virus’ origins, which had ruled lab release “extremely unlikely.” “Theories of accidental release from a lab and zoonotic spillover both remain viable,” the group wrote.
The same month, two former New York Times science journalists penned influential stories backing the lab escape idea, and much of the press has embraced the possibility. President Joe Biden also announced that he was asking U.S. intelligence to issue a new report on the subject by late August.
Despite the increased media attention, little has changed on the ground. There still is no credible evidence that the virus came from a lab in Wuhan, China, where the pandemic began. At the same time, a natural spillover from an animal to a human — the scenario widely viewed as most likely — has not yet been proven.
To some scientists, the lack of evidence about how SARS-CoV-2 emerged has meant little can be concluded either way.
Jesse Bloom, a computational biologist who studies viruses at the Fred Hutchinson Cancer Research Center and the lead author of the letter in Science calling for a more rigorous investigation, told us in an email that he found natural zoonosis and lab accident scenarios involving a researcher being infected with a “natural collected virus” or “experimenting on and possibly growing or modestly modifying a naturally collected virus” all plausible.
“I don’t think there is sufficient evidence to estimate relative probabilities for these scenarios,” he said.
But to many others, the existing data tilts strongly toward a natural spillover.
“[W]hile both lab and natural scenarios are possible, they are not equally likely — precedence, data and other evidence strongly favor natural emergence as a highly likely scientific theory for the emergence of SARS-CoV-2, while the lab leak remains a speculative hypothesis based on conjecture,” Kristian G. Andersen, a professor of immunology and microbiology at Scripps Research, told the New York Times.
“There are still gaps that have to be filled, but I think the evidence we do have right now points to an animal-to-human scenario,” Stephen Goldstein, an evolutionary virologist at the University of Utah who has studied coronaviruses for most of the last decade, told us.
We’ll run through some of the arguments of the lab leak hypothesis and explain why most scientists still suspect a natural origin.
Lab Leak Conjectures
The basic premise of the lab leak hypothesis is that in the course of doing research, a scientist became infected with SARS-CoV-2
