Origin of SARS-CoV-2
Since the beginning of the COVID-19 pandemic, there have been efforts by scientists, governments, and others to determine the origin of the SARS-CoV-2 virus. Similar to other outbreaks, the virus was derived from a bat-borne virus and most likely was transmitted to humans via another animal in nature, or during live wildlife trade such as that in food markets. While other explanations, such as speculations that SARS-CoV-2 was accidentally released from a laboratory have been proposed, such explanations are not supported by evidence. Conspiracy theories about the virus's origin have proliferated widely.
Research is ongoing as to whether SARS-CoV-2 came directly from bats or indirectly through an intermediate host, such as pangolins, civets, or raccoon dogs. Genomic sequence evidence indicates the spillover event introducing SARS-CoV-2 to humans likely occurred in late 2019. As with the 2002–2004 SARS-CoV-1 outbreak, efforts to trace the origins of SARS-CoV-2 have spanned years, with the World Health Organization and independent researchers conducting investigations into the origins of SARS-CoV-2 since 2020, but as of 2025, no conclusive determination has been made regarding its specific geographic and taxonomic origins.
In 2025 the World Health Organization's Scientific Advisory Group for the Origins of Novel Pathogens, and an independent review, concluded that a zoonotic origin has the "weight of available evidence" and emphasized that the origin remains unresolved without additional primary data, including early patient records and sequences, detailed wildlife supply-chain documentation, and laboratory biosafety and health records from Wuhan institutions.
Zoonosis
While there are multiple proposed explanations for how SARS-CoV-2 was introduced into and evolved adaptations suited to human populations, there is significant evidence and agreement that the most likely original viral reservoir for SARS-CoV-2 is horseshoe bats. The closest known viral relatives of SARS-CoV-2 are BANAL-52 and RaTG13, sampled from horseshoe bat droppings in Feuang, Laos, and Yunnan province in China respectively. The evolutionary distance between SARS-CoV-2 and RaTG13 is estimated to be about 50 years.Bats are a significant reservoir species for a diverse range of coronaviruses, and humans have been found with antibodies for them suggesting that direct infection by bats is common. The zoonotic transmission of SARS-CoV-2 virus to humans took place in the context of exacerbating factors that could make such spillovers more likely. Human contact with bats has increased as human population centers encroach on bat habitats. Several social and environmental factors including climate change, natural ecosystem destruction and wildlife trade have also increased the likelihood for the emergences of zoonosis. One study made with the support of the European Union found climate change increased the likelihood of the pandemic by influencing distribution of bat species.
The earliest human cases of SARS-CoV-2 were identified in Wuhan, but the index case remains unknown. RaTG13 was sampled from bats in a mine in Mojiang County, Yunnan, located roughly away from Wuhan, and there are relatively few bat coronaviruses from Hubei province, where Wuhan is located.
Intermediate host
In addition to direct spillover, another pathway, considered highly likely by scientists, is that of transmission through an intermediate host. Specifically, this implies that a cross species transmission occurred prior to the human outbreak and that it had pathogenic results on the animal. This pathway has the potential to allow for greater adaptation to human transmission via animals with more similar protein shapes to humans, though this is not required for the scenario to occur. The evolutionary separation from bat viruses is explained in this case by the virus's presence in an unknown species with less viral surveillance than bats. The virus's ability to easily infect and adapt to additional species provides evidence that such a route of transmission is possible.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.
A 2024 study of samples collected from Huanan Seafood Wholesale Market found genetic material of various possible intermediate hosts. The most likely were raccoon dogs. Additionally, the study suggests the raccoon dogs may have come from southern China, where the closest-known relatives to SARS-CoV-2 were found in bats.
Unlikely scenarios
While the scientific consensus is that SARS-CoV-2 derived from viruses hosted in bats, the precise means by which this occurred has been sometimes subject to speculation. Below are some scenarios judged to be unlikely. Another proposed introduction to humans is through fresh or frozen food products, though scientists do not consider this to be a likely origin of SARS-CoV-2 in humans.Lab leak theory
Investigations
Chinese government
The first investigation conducted in China was by the Wuhan Municipal Health Commission, responding to hospitals reporting cases of pneumonia of unknown etiology, resulting in the closure of the Huanan Seafood Wholesale Market on 1 January 2020 for sanitation and disinfection. The Chinese Center for Disease Control and Prevention entered the market the same day and took samples; as the animals had been removed before public-health authorities came in, no animals were sampled, although that would have been more conclusive.In April 2020, China imposed restrictions on publishing academic research on the novel coronavirus. Investigations into the origin of the virus would receive extra scrutiny and must be approved by Central Government officials. The restrictions do not ban research or publication, including with non-Chinese researchers; Ian Lipkin, a US scientist, has been working with a team of Chinese researchers under the auspices of the Chinese Center for Disease Control and Prevention, a Chinese government agency, to investigate the origin of the virus. Lipkin has long-standing relationships with Chinese officials, including premier Li Keqiang, because of his contributions to rapid testing for SARS in 2003.
The Huanan live-animal market was suspected of being the source of the virus, as there was a major, early cluster of cases there. On 31 January 2021, a team of scientists led by the World Health Organization visited the market to investigate the origins of COVID-19. Based on the existing evidence, the WHO concluded that the origin of the virus was still unknown, and the Chinese government insisted that the market was not the origin. The Chinese government has long insisted that the virus originated outside China, and until June 2021 denied that live animals were traded at the Huanan market.
Some Chinese researchers had published a preprint analysis of the Huanan swab samples in February 2022, concluding that the coronavirus in the samples had likely been brought in by humans, not the animals on sale, but omissions in the analysis had raised questions, and the raw sample data had not yet been released.
On March 4, 2023, the data from the swab samples of the Huanan live-animal market were released, or possibly leaked; a preliminary analysis of this data was reviewed by the international research community, which said that it made an animal origin much more likely. Although the samples do not definitively prove that the raccoon dog is the "missing" intermediate animal host in the bat-to-human transmission chain, it does show that common raccoon dogs were present in the Huanan market at the time of the initial SARS-CoV-2 outbreak, in areas that were also positive for SARS-CoV-2 RNA, and substantially strengthens this hypothesis as the proximal origin of the pandemic.
An attempt by these researchers to collaborate with the Chinese researchers was not answered, but the raw data was removed from the online database. On March 14, an international group of researchers presented a preliminary analysis at a meeting of the World Health Organization's Scientific Advisory Group for Origins of Novel Pathogens, at which Chinese COVID-19 researchers were also present. On the sixteenth, George Gao, the former head of the CCDC and lead author on the February 2022 preprint, told Science that there was "nothing new" in the raw data, and refused to answer questions about why his research team had removed it from the database.
On March 17, the WHO director-general said that the data should have been shared three years earlier, and called on China to be more transparent in its data-sharing. There exists further data from further samples which has not yet been made public. Maria Van Kerkhove, the WHO's COVID-19 technical lead, called for it to be made public immediately.
After April 2023, Chinese authorities and China-based researchers issued several new outputs relevant to origin-tracing. In 2024 the Chinese Center for Disease Control and Prevention published a peer-reviewed report on its surveillance of the Huanan Seafood Wholesale Market in Wuhan. The study reported 74 positive environmental samples out of 923 by RT-qPCR or sequencing, three successful virus isolations from market swabs, no positives among 457 animal samples collected after the market closed, and detection of lineage A in one environmental sample. The authors concluded that contamination of the market environment likely reflected shedding by infected people, and they deposited raw sequence data to Chinese and international repositories.
On April 30, 2025 the State Council Information Office released a white paper, "Covid-19 Prevention, Control and Origins Tracing: China's Actions and Stance." It asserted that Wuhan was not the natural origin of SARS-CoV-2 and described a laboratory incident as "extremely unlikely." The document summarized Chinese analyses of early Wuhan patients, a 2019 Wuhan blood-donor serosurvey that found no specific antibodies, extensive wildlife screening that did not detect SARS-CoV-2, and investigations that treated cold-chain introduction as a possible route for the virus's arrival in China. The document called for further origin-tracing outside China.
Following the WHO Scientific Advisory Group for the Origins of Novel Pathogens independent assessment on June 27, 2025, which requested additional primary data from China regarding the Wuhan outbreak, the National Health Commission stated that it did not approve parts of the report and said it contained "false information based on subjective speculation," while reaffirming conclusions of the 2021 joint WHO-China study. As of June 27, 2025 WHO continued to report that investigations into the Wuhan origins remained incomplete and that China had not provided several requested datasets and records, including early patient sequences from Wuhan, Huanan market supply-chain information, and laboratory biosafety documentation from Wuhan research facilities.