The exact origin of SARS-CoV-2, the virus that causes the disease COVID-19, remains unknown. The scientific consensus has been that the virus likely originated in bats and then jumped to humans either directly or indirectly, through contact with an animal. Such zoonotic transfers have happened before with the coronaviruses responsible for SARS and MERS. Lacking proof of that transfer, however, some scientists say more investigation is needed, and that there could have been an accidental laboratory leak, either of a naturally occurring virus or a lab-enhanced one.
The virus is indeed similar to bat coronaviruses. Researchers in China have said SARS-CoV-2 shares 96% of its genome with a bat virus. Other teams have turned up multiple other bat viruses that are more closely related, once factoring in the viral habit of exchanging chunks of genetic material. No precursor virus, however, has been identified.
An article published in Nature Medicine in March 2020 found that SARS-CoV-2 “is not a laboratory construct or a purposefully manipulated virus.” The authors, who analyzed genomic data, said that the virus likely originated through “natural selection in an animal host before zoonotic transfer,” or “natural selection in humans following zoonotic transfer.”
The authors said an accidental laboratory release of the naturally occurring virus can’t be ruled out, but they “do not believe that any type of laboratory-based scenario is plausible.”
But on May 14, 2021, the journal Science published a letter from 18 scientists calling for “more investigation” to determine the pandemic’s origin. “Theories of accidental release from a lab and zoonotic spillover both remain viable,” they wrote. “Knowing how COVID-19 emerged is critical for informing global strategies to mitigate the risk of future outbreaks.”
Many scientists with expertise in coronaviruses nevertheless consider a lab escape unlikely, and a leak of an engineered virus highly implausible, if not impossible.
The earliest known human cases of the disease occurred in late 2019 in Wuhan, China. Chinese officials reported an outbreak of mysterious pneumonia cases to the World Health Organization on Dec. 31, 2019.
Updated, July 1: We updated this item to incorporate findings from our story “The Facts – and Gaps – on the Origin of the Coronavirus.”