investigations into the origin of covid-19 investigations into the origin of covid-19 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. most scientists agree that, as with many other pandemics in human history, the virus is likely derived from a bat-borne virus transmitted to humans in a natural setting. many other explanations, including several conspiracy theories, have been proposed. some scientists and politicians have speculated that sars-cov-2 was accidentally released from a laboratory. this theory is not supported by evidence. part of a series on thecovid-19 pandemicscientifically accurate atomic model of the external structure of sars-cov-2. each "ball" is an atom. covid-19 (disease) sars-cov-2 (virus) cases deaths timeline 2019 2020 january responses february responses march responses april responses may responses june responses july responses august responses september 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association football baseball basketball combat sports cricket disc golf gaelic games gridiron football ice hockey motorsport rugby league impacts animals black people crime death rates by country disability domestic violence emergency evacuations education female environment hospitals language lgbt community long-term care media coverage mental health symptoms migration military notable deaths other health issues politics diplomacy popular culture protests pregnancy prisons religion catholic church hajj science and technology social media strikes suicides telehealth xenophobia and racism society ireland malaysia new zealand russia uk us covid-19 portal sars-cov-2 has close genetic similarity to multiple previously identified bat coronaviruses, suggesting it crossed over into humans from bats. research is ongoing as to whether sars-cov-2 came directly from bats or indirectly through an intermediate host, such as pangolins, civets, treeshrews, 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 specific geographic and taxonomic origins of sars-cov-2 could take years, and results may be inconclusive. in 2021, the world health assembly (on behalf of the who) commissioned a study conducted jointly between who experts and chinese scientists. echoing the assessment of most virologists, the study concluded that the virus most likely had a zoonotic origin in bats, possibly via an intermediate host. it also stated that a laboratory origin for the virus was "extremely unlikely". who director-general tedros adhanom ghebreyesus, in concert with various governments including the us and the eu, responded to the 2021 study report saying the matter still "requires further investigation". in june 2022, a second round of investigations concluded that more investigations in the various possible pathways of emergence were necessary. in july 2021, zeng yixin, vice health minister of the chinese national health commission, said that china would not participate in a second phase of investigation, denouncing the decision to proceed as "shocking" and "arrogant". in response to the who's june 2022 report, chinese foreign ministry spokesperson zhao lijian called the lab leak theory "a lie concocted by anti-china forces for political purposes, which has nothing to do with science". 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. origin scenarios the origin of sars-cov-2 has been the subject of debate. there are multiple proposed explanations for how sars-cov-2 was introduced into, and evolved adaptations suited to, the human population. there is significant evidence and agreement that the most likely original viral reservoir for sars-cov-2 is horseshoe bats, with the closest known viral relatives being ratg13 and banal-52, sampled from horseshoe bat droppings in yunnan province in china and feuang, laos, respectively. the evolutionary distance between sars-cov-2 and ratg13 is estimated to be about 50 years (between 38 and 72 years). the earliest human cases of sars-cov-2 were identified in wuhan, but the index case remains unknown. ratg13 was sampled from bats in yunnan, located roughly 1,300 km (810 mi) away from wuhan, and there are relatively few bat coronaviruses from hubei province. each origin hypothesis attempts to explain this gap in virus evolution and location a different way. these scenarios continue to be investigated to identify the definitive origin of the virus. direct zoonotic transmission in a natural setting further information: zoonosis the most direct pathway of introduction is direct zoonotic transmission (also known as spillover) from the reservoir species to humans. scientists consider this to be a highly likely origin of the sars-cov-2 virus in humans. human contact with bats has increased as human population centers encroach on bat habitats, leading to increased opportunities for spillover. bats are a significant reservoir species for a diverse range of coronaviruses, and humans have been found with antibodies for them suggesting that this form of direct infection by bats is common. however, in this scenario, the direct ancestor of sars-cov-2 remains undiscovered in bats. several social and environmental factors including climate change, natural ecosystem destruction and wildlife trade 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. 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' presence in an unknown species with less viral surveillance than bats. the virus' ability to easily infect and adapt to additional species (including mink) provides evidence that such a route of transmission is possible. cold/food chain another proposed introduction to humans is through fresh or frozen food products, referred to as the cold/food chain. scientists do not consider this to be a likely origin of sars-cov-2 in humans. this scenario's source animal could be either a direct or intermediary species as described above. many investigations centered around the huanan seafood wholesale market in wuhan, which had an early cluster of cases. while there have been food-borne outbreaks of human viruses in the past, and evidence of re-introduction of sars-cov-2 into china through imported frozen foods, investigations found no conclusive evidence of viral contamination in products at the huanan market. laboratory incident this section is an excerpt from covid-19 lab leak theory. the wuhan institute of virology in wuhan, china the covid-19 lab leak theory, or lab leak hypothesis, is the idea that sars-cov-2, the virus that caused the covid-19 pandemic, is the result of a laboratory leak. the theory is highly controversial; most scientists believe the virus spilled into human populations through natural zoonosis, similar to the sars-cov-1 and mers-cov outbreaks, and consistent with other pandemics in human history. available evidence suggests that the sars-cov-2 virus was originally harbored by bats, and spread to humans multiple times from infected wild animals at the huanan seafood market in wuhan, hubei, china, in december 2019. there is no evidence sars-cov-2 existed in any laboratory prior to the pandemic. an original animal reservoir has not yet been confirmed, though several candidate species have been identified. central to many versions of the lab leak theory is suspicion about the proximity of the outbreak to a virology institute that studies coronaviruses, the wuhan institute of virology (wiv). however, most large chinese cities have laboratories which study coronaviruses, and wuhan is one of the largest cities in china. virus outbreaks tend to 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 idea has been informed by (and has, in turn, fueled) racist and xenophobic sentiments. scientists from wiv had previously collected sars-related coronaviruses from bats in the wild; allegations that they also performed undisclosed risky 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. mojiang mine incident another proposed origin scenario relates to a 2012 incident involving six miners in an abandoned mining cave near the town of tongguan in mojiang county, yunnan, china. six miners cleaning bat feces fell ill, three of whom died from fatal pneumonia. out of concerns that the miner's cases could represent a novel disease, serum samples collected from the miners were sent to the wuhan institute of virology and tested by shi zhengli and her group for various fatal viruses including ebola virus, nipah virus, and sars-related coronaviruses. the samples tested negative. in order to uncover other possible causes of the infection, animals (including bats, rats, and musk shrews) were sampled in and around the cave by shi's group. one such sample from the droppings of rhinolophus affinis (intermediate horseshoe bat) contained a novel rna sequence later identified as "ratg13", which previously (in 2020) was described as the closest relative of sars-cov-2 in nature (sharing 96.1% nucleotide identity). in 2022, though, a closer relative to sars-cov-2 was discovered by scientists from the pasteur institute while conducting field work in feuang, laos sampling horseshoe bats: banal-52 (96.8% identity). members of drastic, a collection of internet activists, have speculated that ratg13 could have been a backbone for reverse genetics experiments which they believe created sars-cov-2. scientists have said ratg-13 is too distantly related to be connected to the pandemic's origins, and could not be altered in a laboratory to create sars-cov-2, due to this considerable genetic distance and the amount of time, effort, and resources required for one virus to be mutated into the other. others have hypothesized that visiting researchers from the wuhan institute of virology entered the mine and also fell ill with the disease, and later passed it into the general population. this idea has been criticized by scientists in several ways: sars-cov-2 has never been detected in the mine, the symptoms displayed by the miners that contracted the disease in 2012 were not typical of covid-19 symptoms, and it is exceptionally unlikely, given the nature of the virus, that it would have infected so few people between 2012 and 2019 and only reached epidemic proportions after seven years. 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