A new World Health Organization report investigating the origins of the coronavirus has raised more questions than answers about how and where the virus that exploded in a global pandemic arose.
The report, published on March 30, offsets where the evidence currently points: the virus, called SARS-CoV-2, probably jumped people from bats through another animal; it is unlikely to come from a laboratory. But officials still cannot demonstrate or rule out any scenario. And questions about how much access to potential evidence an international team of experts had on their 28-day trip to Wuhan, China, in January and February cast a shadow over the findings.
On that trip, 17 WHO experts joined 17 Chinese scientists to assess four potential scenarios of the origins of the coronavirus. The team concluded that the two main scenarios are the transmission of the virus to people directly from bats or, most likely, through an intermediate animal such as a civet dog or a raccoon.
A third possibility is that the virus reaches people through contaminated frozen products, which the team considers less likely, but which deserves more research. The latest researchers wrote that the latest scenario, that the virus began to spread among people after a lab accident, was "highly unlikely."
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In a joint statement on March 30, 14 countries, including the United States, expressed concern that the WHO team was delayed and lacked access to original data and samples from people and animals. That reaction comes amid reports that the Chinese government had a hand in the mission, monitoring the sites the team accessed during the visit and report writing. “Scientific missions like these should be able to do their job in conditions that produce independent and objective recommendations and discoveries,” the countries wrote in the statement.
Some explanations may be more likely than others, but for now all possibilities remain on the table, says WHO Director-General Tedros Adhanom Ghebreyesus. The report raised issues that require further study, such as additional work to identify the first cases of COVID-19, he noted at a March 30 meeting with WHO member states. He also said that when it was hypothesized that the virus came from a lab accident, "I don't think this assessment was extensive enough. More data and studies will be needed to come to more solid conclusions."
“This report is a very important beginning, but it is not the end,” he added. "We have not yet found the source of the virus and we must follow science and leave no stone unturned. Finding the source of a virus takes time. … No research trip can provide all the answers."
For now, here are four great takes from the 120-page report:
1. Markets are the most likely source of significant virus transmission.
The focus is again on the markets that sell animals.
COVID-19 made its global debut amid a group of cases related to the Huanan fish market in Wuhan in late December 2019. Researchers tested hundreds of animals in and around the market to detect coronavirus, including animals for sale as rabbits. , hedgehogs, salamanders and birds – but none tested positive. Neither did thousands of domestic or wild animals in and around Wuhan. In addition, some initial cases of COVID-19 that experts later identified, after the coronavirus began to spread in other countries, were unrelated to the market.
Together, the findings hinted that the market may have helped the virus spread among people due to the large crowd, but that the Huanan Seafood market was not the original source.
It is possible that other markets also played a role in the spread of the virus. The first known case of COVID-19 was in a person who started showing symptoms on December 8, 2019. That person was not associated with the Huanan market but had recently visited another market.
Overall, of 174 people sick with COVID-19 in December, more than half had recently gone to a market, where they could be exposed. An additional 26 percent was exposed to meat and fish or frozen products.
The failure so far to find an animal that tests positive for SARS-CoV-2 shows how difficult it is to identify specific species as a potential host, said Peter Ben Embarek, lead researcher on the WHO mission and food safety expert. March 30 press conference. The hunt for where the viruses came from takes time, sometimes years (SN: 18/03/21).
Future studies should expand the search for infected animals to wildlife farms that have supplied products to markets linked to COVID-19 cases. People working on farms and those who handled the products should also be tested for antibodies to see if they have ever had coronavirus infections, the team suggests.
2. It is likely that the coronavirus would not have circulated long before December 2019
There is still no evidence that the virus spread widely among people before the first documented case of COVID-19 in early December, the WHO team discovered.
The researchers combed more than 76,000 clinical records from October to November 2019. Within these records, there were 92 possible cases of COVID-19. But 67 of those people had no signs of an infection based on antibody tests done a year later. And the 92 were eventually discarded based on the clinical criteria of COVID-19. However, the records would not include mild cases in people who have never been to the hospital, so there are possible gaps in the tests.
Additional evidence from isolated cases in countries outside China in late 2019 hinted that the virus had spread to those places before COVID-19 was first detected in Wuhan. But those reports have not yet been confirmed, the team wrote.
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The time when the virus began to spread in China is in line with a recent study that analyzed genetic data and simulated the early days of the pandemic to estimate when the virus may have emerged. The animal-to-human spill could have occurred between mid-October and mid-November 2019, Joel Wertheim and colleagues reported on March 18 in Science.
After the virus is transmitted from animals to humans, cases in people with mild symptoms can help them fly under the radar until December, when some people have fallen seriously ill, says Wertheim, an evolutionary biologist and molecular epidemiologist at the University of California, San Diego. .
What’s more, the pandemic itself was far from inevitable, Wertheim says. In the simulations, more than two-thirds of SARS-CoV-2 transmissions from animals to humans were extinguished, causing only a few infections in people before they died. "Even a virus capable of causing a pandemic kneeling the world was not necessarily a lost conclusion."
3. The "laboratory leak" hypothesis is unlikely, though difficult to disprove altogether
Based on a visit to the Wuhan Institute of Virology and interviews with scientists working there, the report concludes that the virus probably did not start in a laboratory. Although some experts requested a full audit of the institute’s labs, the WHO mission was not designed to conduct a forensic investigation, WHO’s Ben Embarek said at the March 30 press conference.
Researchers at the institute considered the possibility of laboratory leaks at the start of the pandemic and recorded institute records but found no evidence that anyone worked with a SARS-CoV-2-like virus, Ben Embarek said. In addition, antibody tests did not reveal any employees with signs of having ever had a coronavirus infection.
The lab leak "is possible, but there is no evidence to support it," says Massa Shoura, a biophysicist and genomics expert at Stanford University who did not participate in the report. Other coronaviruses that have caused SARS and MERS have made the leap to humans from animals, so it makes sense that it would also be the most likely route for SARS-CoV-2.
However, it can be extremely difficult to accumulate data to prove that it is negative. “I don’t think we’re able to provide enough evidence to convince people who are convinced that he escaped from a lab that he isn’t,” Wertheim says. "Even if you find a virus literally identical to SARS-CoV-2 (in animals) … they could still argue that that virus had been found and isolated and introduced into a lab and escaped as it was."
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4. Experts are far from knowing the origins of coronavirus
Overall, the report offers few clear conclusions about the onset of the pandemic. Rather, it provides context for the possibilities and helps to delve deeper into the studies that researchers should address below.
Still, more than a year has passed since the virus made its leap to humans. That time lapse can make research difficult if SARS-CoV-2 no longer circulates in its dam, the animals that originally housed it.
“We have to be prepared so that we never find the natural deposit of this virus,” Wertheim says. But sometimes all it takes is a good sample to give researchers important clues. Maybe it’s a casual encounter with the right animal during a wildlife survey or trying out the right market people.
Taking it a step further, researchers need to better understand the diversity of coronaviruses in bats and other wildlife species in Southeast Asia, Shoura says. That means compiling a “dictionary” of the viruses found there to help researchers track the history of viral evolution, something the WHO team also recommends.
“We just scratch the surface of these studies so complex that it has to be done,” Ben Embarek said.