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It may seem strange that more than a year after the emergence of the coronavirus SARS-CoV-2 and the COVID-19 pandemic it created we are still debating the origins of the virus. The question remains important, however, and recently the World Health Organization (WHO) and Chinese scientists concluded their investigation into those origins. The report was frustratingly less than conclusive.

The investigation was actually launched in May of 2020, with groundwork investigations beginning in July. Final investigations in China were completed earlier this year, and the full report was just published. According to the report:

The joint international team comprised 17 Chinese and 17 international experts from other countries, the World Health Organization (WHO), the Global Outbreak Alert and Response Network (GOARN), and the World Organisation for Animal Health (OIE) (Annex B). The Food and Agriculture Organization of the United Nations (FAO) participated as an observer. Following initial online meetings, a joint study was conducted over a 28-day period from 14 January to 10 February 2021 in the city of Wuhan, People’s Republic of China.

Let’s review the main findings, keeping in mind that science is often a matter of probability. There was no smoking gun proving a specific origin, and the team has had to rely on scientific inference.

One focus of the investigation was simply tracking the emergence of COVID-19. The team found no evidence of an increase in pneumonia-like illness, all-cause mortality, or even purchase of medications to treat fever or respiratory symptoms prior to the emergence of illness in Wuhan in late 2019. Increase in hospitalizations and deaths started to rise in Wuhan in January 2020, and then later outside Wuhan but within Hubei Province. So the evidence does support the emergence of COVID-19 in and around Wuhan. Further, extensive review of hospital records did not find any likely cases of COVID-19 in October or November 2019 in Wuhan, so it was likely not circulating prior to its emergence in December.

That was the epidemiological evidence. Scientists on the team also looked at molecular evidence – studying the virus itself. They found:

Evidence from surveys and targeted studies so far have shown that the coronaviruses most highly related to SARS-CoV-2 are found in bats and pangolins, suggesting that these mammals may be the reservoir of the virus that causes COVID-19. However, neither of the viruses identified so far from these mammalian species is sufficiently similar to SARS-CoV-2 to serve as its direct progenitor. In addition to these findings, the high susceptibility of mink and cats to SARS-CoV2 suggests that additional species of animals may act as a potential reservoir.

This supports the prior conclusion that SARS-CoV-2 is a zoonotic virus – coming from an animal reservoir. The scientists think it is likely that the virus originated in bats but came to humans through another species, as yet unidentified. This is supported by other investigations finding that SARS-CoV-2-related coronaviruses are endemic in the bat and pangolin populations of Southeast Asia. However, SARS-CoV-2 itself was not found in any wild or domestic animal population in China. So it did not come directly from an animal reservoir, but mutated to SARS-CoV-2 as it jumped to humans, probably through an intermediary species.

Molecular analysis can also track the viral strains as they spread. Fortunately Hunan hospitals kept samples from early patients, so those viruses could be studied. They found that there was likely a cluster of cases from the Huanan meat market, but that was not the origin of the virus as different strains were already circulating. They also calculated the time to the most recent common ancestor of all the early strains, which dates to probably late November to early December 2019. An earlier origin in October cannot be ruled out, however.

A lot of attention was paid to the Huanan market as a possible origin of the virus. They did find many samples from the market that were contaminated with SARS-CoV-2. They could have been contaminated by people in the market already sick with COVID-19. Also, the market included cold-chain meats and products from 20 different countries. It is possible that the virus came to that market through one of these cold chains, although no evidence of a specific source of contamination was found. The virus can survive in frozen meats, however, so this possibility remains plausible.

Through their direct investigation and review of the published literature, the WHO team considered four possible sources for COVID-19 and the likelihood of each:

  • direct zoonotic spillover is considered to be a possible-to-likely pathway;
  • introduction through an intermediate host is considered to be a likely to very likely pathway;
  • introduction through cold/food chain products is considered a possible pathway;
  • introduction through a laboratory incident was considered to be an extremely unlikely pathway

Of course, the “extremely unlikely pathway” of a lab accident has received a lot of media attention, which is understandable. The investigators could not rule out a lab origin, but there was no direct evidence for it, and the totality of evidence from epidemiology and molecular biology make it the least likely scenario. The joint WHO-China findings have received some international criticism. In a joint statement of 14 countries, including the US, the WHO and China were urged to provide full transparency, and criticized the mission for: “significantly delayed and lacked access to complete, original data and samples”.

This leaves the door open that China was hiding data that may have pointed to a lab origin for SARS-CoV-2. Many have pointed to the Wuhan Institute for Virology, which is the world’s expert on bat-derived coronaviruses. This may seem like a coincidence, but it is not surprising that a research lab will exist in a part of the world where such viruses exist. In other words, both the location of the lab and the COVID-19 outbreak may be related to the fact that zoonotic coronaviruses are endemic to the region. But still, the coincidence is noted.

Examinations of the virus itself have not revealed any smoking gun of genetic manipulation. But results have been conflicting about the potential for a lab origin. Some published studies have concluded that the virus is incompatible with a lab origin. Other studies conclude that genetic manipulation cannot be ruled out. This is why many pinned hopes on the WHO team to resolve the debate, which they did not do definitively. For now we will have to be content with “extremely unlikely”, and continue for calls for fuller, more transparent research to finally put the question to bed.

All of this matters for various reasons. Experts are already warning that pandemics like COVID-19 are likely going to be more common going forward. The world is much more interconnected than ever before, we are living closer to natural habitats (some might say invading), and there is a global trade in animals parts. All of these factors conspire to make the occurrence and spread of zoonotic infections, including developing into full-blown pandemics, more likely. COVID-19 is far from the most deadly disease out there, and this pandemic is likely a dress-rehearsal for worse pandemics to come.

Unless, of course, we make some changes. One major goal of the WHO study was to identify possible sources of the pandemic, in hopes of producing actionable items to limit the risk of future pandemics. Further, the report produced an international call for full cooperation and transparency. We now all know in a very visceral way that things that happen in distant parts of the world can come to our shores and dramatically affect us. In a very real sense, we are all in this together, and we have to work together to have a much better reaction to the next pandemic.

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Posted by Steven Novella

Founder and currently Executive Editor of Science-Based Medicine Steven Novella, MD is an academic clinical neurologist at the Yale University School of Medicine. He is also the host and producer of the popular weekly science podcast, The Skeptics’ Guide to the Universe, and the author of the NeuroLogicaBlog, a daily blog that covers news and issues in neuroscience, but also general science, scientific skepticism, philosophy of science, critical thinking, and the intersection of science with the media and society. Dr. Novella also has produced two courses with The Great Courses, and published a book on critical thinking - also called The Skeptics Guide to the Universe.