COVID-19 lab leak theory
The COVID-19 lab leak theory is the hypothesis that SARS-CoV-2, the virus responsible for the COVID-19 pandemic, originated from a laboratory. This claim is highly controversial. There is scientific consensus that the virus is not the result of genetic engineering. Most scientists believe it spread to human populations through natural zoonotic transmission from bats, similar to the SARS-CoV-1 and MERS-CoV outbreaks and consistent with other pandemics throughout human history. Available evidence indicates that SARS-CoV-2 was originally harbored by bats and transmitted to humans through infected wild animals serving as intermediate hosts at the Huanan Seafood Market in Wuhan, Hubei, China, in December 2019. Several candidate animal species have been identified as potential intermediaries. There is no evidence supporting laboratory involvement, no indication that the virus existed in any lab prior to the pandemic, and no record of suspicious biosecurity incidents.
Many scenarios proposed for a lab leak are characteristic of conspiracy theories. Central to many is a misplaced suspicion based on the proximity of the outbreak to the Wuhan Institute of Virology, where coronaviruses are studied. Most large Chinese cities have laboratories that study coronaviruses, and virus outbreaks typically begin in rural areas, but are first noticed in large cities. If a coronavirus outbreak occurs in China, there is a high likelihood it will occur near a large city, and therefore near a laboratory studying coronaviruses. The idea of a leak at the WIV also gained support due to secrecy during the Chinese government's response. The lab leak theory and its weaponization by politicians have both leveraged and increased anti-Chinese sentiment. Scientists from WIV had previously collected virus samples from bats in the wild, and allegations that they also performed undisclosed work on such viruses are central to some versions of the idea. Some versions, particularly those alleging genome engineering, are based on misinformation or misrepresentations of scientific evidence.
The idea that the virus was released from a laboratory appeared early in the pandemic. It gained popularity in the United States through promotion by conservative personalities in early 2020, fomenting tensions between the U.S. and China. Scientists and media outlets widely dismissed it as a conspiracy theory. The accidental leak idea had a resurgence in 2021. In March, the World Health Organization published a report which deemed the possibility "extremely unlikely", though the WHO's director-general said the report's conclusions were not definitive. Subsequent plans for laboratory audits were rejected by China.
Most scientists are skeptical of the possibility of a laboratory origin, citing a lack of any supporting evidence for a lab leak and the abundant evidence supporting zoonosis. Though some scientists agree a lab leak should be examined as part of ongoing investigations, politicization remains a concern. In July 2022, two papers published in Science described novel epidemiological and genetic evidence that suggested the pandemic likely began at the Huanan Seafood Wholesale Market and did not come from a laboratory.
Background
The principal hypothesis for the origin of COVID-19 is that it became infectious to humans through a natural spillover event, which is supported by available evidence. The origin of COVID-19 is not definitively known, and the theory it became infectious to humans through escape from a laboratory where it was being studied has not been definitively ruled out, however most scientists believe zoonosis is more likely, with a minority favoring the lab leak theory. Arguments used in support of a laboratory leak have been described as characteristic of conspiratorial thinking.A 2024 survey of 168 experts, most of whom were epidemiologists and virologists, found on average they viewed zoonosis as 77% likely and a lab leak as 21% likely.
Zoonosis
Most new infectious diseases begin with a spillover event from animals. These spill overs occur spontaneously, either by contact with wildlife animals, which are the majority of cases, or with farmed animals. For example, the emergence of Nipah virus in Perak, Malaysia, and the 2002 outbreak of SARS-CoV-1 in Guangdong province, China, were natural zoonosis traced back to wildlife origin. COVID-19 is considered by scientists to be "of probable animal origin". It has been classified as a zoonotic disease. Some scientists dispute this classification, since a natural reservoir has not been confirmed. The original source of viral transmission to humans remains unclear, as does whether the virus became pathogenic before or after a spillover event.Bats, a large reservoir of betacoronaviruses, are considered the most likely natural reservoir of SARS‑CoV‑2. Differences between bat coronaviruses and SARS‑CoV‑2 suggest that humans may have been infected via an intermediate host. Research into the natural reservoir of the virus that caused the 2002 SARS outbreak has resulted in the discovery of many SARS-like coronaviruses circulating in bats, most found in horseshoe bats. Analysis indicates that a virus collected from Rhinolophus affinis in a cave near the town of Tongguan in Yunnan province, designated RaTG13, has a 96% resemblance to SARS‑CoV‑2. The RaTG13 virus genome was the closest known sequence to SARS-CoV-2 until the discovery of BANAL-52 in horseshoe bats in Laos, but it is not its direct ancestor. Other closely related sequences were also identified in samples from local bat populations in Yunnan province. One such virus, RpYN06, shares 97% identity with SARS-CoV-2 in one large part of its genome, but 94% identity overall. Such "chunks" of very highly identical nucleic acids are often implicated as evidence of a common ancestor.
An ancestor of SARS-CoV-2 likely acquired "generalist" binding to several different species through adaptive evolution in bats and an intermediate host species. Estimates based on genomic sequences and contact tracing have placed the origin point of SARS-CoV-2 in humans as between mid-October and mid-November 2019. Some scientists have suggested slow, undetected circulation in a smaller number of humans before a threshold event could explain an undetected adaption period.
The first known human infections from SARS‑CoV‑2 were discovered in Wuhan, China, in December 2019. Because many of the early infectees were workers at the Huanan Seafood Market, it was originally suggested that the virus might have originated from wild animals sold in the market, including civet cats, raccoon dogs, bats, or pangolins. Subsequent environmental analyses demonstrated the presence of SARS-CoV-2 in the market, with highest prevalence in areas of the market where animals known to be susceptible to SARS-CoV-2 infection were held. Early human cases clustered around the market, and included infections from two separate SARS-CoV-2 lineages. These two lineages demonstrated that the virus was actively infecting a population of animals in the market, and that sustained contact between those animals and humans had allowed for multiple viral transmissions into humans. All early cases of COVID-19 were later shown to be localized to the market and its immediate vicinity.
While other wild animals susceptible to SARS-CoV-2 infection are known to have been sold at Huanan, no bats or pangolins were sold at the market.
Wuhan Institute of Virology
The Wuhan Institute of Virology and the Wuhan Center for Disease Control are located within miles of the original focal point of the pandemic, Wuhan's Huanan Seafood Wholesale Market, and this very proximity has made it easy for conspiracy theories to take root suggesting the laboratory must be the virus' origin. However virology labs are often built near potential outbreak areas. Proponents of the lab leak theory typically omit to mention that most large Chinese cities have coronavirus research laboratories. Virus outbreaks tend to begin in rural areas, but are first noticed in large cities. Stephan Lewandowsky and colleagues write that the location of the Institute near the outbreak site is "literally a coincidence" and using that coincidence as a priori evidence for a lab leak typifies a kind of conjunction fallacy. Furthermore, they observe that is ironic lab leak proponents are keen to argue for the significance of proximity of laboratories to the outbreak, while ignoring the proximity of wet markets, which have long-been identified as potential origins for viral spillover events.The Wuhan Institute of Virology had been conducting research on SARS-like bat coronaviruses since 2005, and was involved in 2015 experiments that some experts have characterized as gain-of-function. Others have disputed the characterization, pointing out that the experiments in question were not conducted at the WIV, but at UNC Chapel Hill, whose institutional biosafety committee assessed the experiments as not "gain-of-function". Baric did acknowledge the risks involved in such studies, writing, "Scientific review panels may deem similar studies building chimeric viruses based on circulating strains too risky to pursue... The potential to prepare for and mitigate future outbreaks must be weighed against the risk of creating more dangerous pathogens."
The fact that the lab is in Wuhan, the city where the pandemic's early outbreak took place, and the fact that the research at WIV was being conducted under the less stringent biosafety levels 2 and 3, has led to speculation that SARS-CoV-2 could have escaped from the Wuhan lab. Richard Ebright said one reason that lower-containment BSL-2 laboratories are sometimes used is the cost and inconvenience of high-containment facilities. Australian virologist Danielle Anderson, who was the last foreign scientist to visit the WIV before the pandemic, said the lab "worked in the same way as any other high-containment lab". She also said it had "strict safety protocols". The Huanan Seafood Market may have only served as a jumping off point for a virus that was already circulating in Wuhan, facilitating rapid expansion of the outbreak.