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Amid untold suffering, the coronavirus pandemic, which has killed at least 1.8 million people over the past year, has been an era of remarkable scientific breakthroughs, including record-breaking vaccine development programs.

But the answer to one of the fundamental questions about the virus remains shrouded in mystery: How did a pathogen found in bats make the jump to humans, presumably in or near the Chinese city of Wuhan, where it was first detected in late 2019?

An upcoming World Health Organization mission to China intends to investigate the matter.

That is, if it ever actually sets foot in China. WHO officials have been negotiating with Beijing to allow a team of international experts to investigate the virus’s origin for almost a year, but Director General Tedros Adhanom Ghebreyesus said this week that China was still holding up the process.

In the void of information about the virus’s origin, speculation has grown. Chinese officials have suggested that the virus might not have originated in their country, while U.S. officials have said repeatedly that the virus could have leaked from a lab in Wuhan.

In such a politicized and conspiratorial atmosphere, some virologists and public health experts now have doubts that a clear picture of the virus’s origins can ever be discovered. But there are still reasons to hope that the WHO mission can proceed and succeed.

Search for the missing link

In interviews, the WHO team has emphasized that it does not intend to go into the mission with preconceived notions.

Everything is on the table,” Peter Ben Embarek, a Danish food safety expert and head of the mission, told my colleague Emily Rauhala during an interview last week. The team would begin with a “basic study that will give us clues, and those clues will then help us test different hypotheses.”

Ben Embarek did say that one scenario would be the “least surprising” — that the virus now known as SARS-CoV-2, or the novel coronavirus, had spread from bats to an unidentified second animal before infecting humans through zoonotic spillover.

Among scientists, this is the apparent consensus. “The virus is just like a virus we would expect to see in wild bat populations, similar viruses have jumped from non-human animals to animals in the past, so I see no reason to speculate about this any further,” Andrew Rambaut, a microbiologist at the University of Edinburgh, told Today’s WorldView last year.

If it could be proved, this jump from a bat to another animal before humans could explain how the virus made it from the Chinese province of Yunnan, where scientists found its closest relative some time ago (a virus known as SARS-CoV RaTG13), to Wuhan, in Hubei province, more than 1,000 miles away.

But a key question remains: What, and where, was the intermediary animal? Without knowing the answer, scientists have fewer tools to prevent the same thing from happening again.

Around the world, experts have already seen that the virus can spread to and from animals including minks, prompting costly mass cullings.

The WHO team is expected to focus much of its investigation on the Huanan Seafood Market in central Wuhan, to which many early coronavirus cases were linked.

The delay in finding the animal in question is not without precedent. Ben Embarek noted that it took roughly a year to link Middle East respiratory syndrome, or MERS, to dromedary camels.

Sorting theory from fact

While most virologists favor the theory of zoonotic spillover, other, more controversial theories abound.

In recent weeks, for example, Chinese officials have pushed the idea that the virus came from outside the country.

High-level experts such as Wu Guizhen, biosafety expert at the Chinese Center for Disease Control and Prevention, have said that focusing on wildlife may be the wrong approach. “When we were investigating the origins of the virus, we kept looking for the intermediary host,” Wu said in June. “Now, we may need to reexamine whether the virus really did come from wild animals.”

Meanwhile, a rival theory suggests that the virus could have escaped from the Wuhan branch of the Chinese Center for Disease Control and Prevention, which did conduct research on bat coronaviruses.

That idea became popular among hawkish Republican lawmakers such as Sen. Tom Cotton (R-Ark.) last year, but it never really went away: As recently as last week, deputy national security adviser Matthew Pottinger was reported to have told British lawmakers that there was “a growing body of evidence” that this was a “a credible possibility.”

The idea also gained mainstream prevalence with a recent New York Magazine story, which detailed the hypothesis that the virus had unintentionally leaked from the laboratory during controversial “gain of function” experiments, wherein viruses are manipulated to see how they can become more virulent and transmissible.

Virologists tend to be skeptical of both of these theories, noting that they come with political notions attached and that direct evidence for either is lacking.

The WHO team has pledged to consider them, but Ben Embarek said he had his doubts about both. The idea that the virus could have been imported to China a year ago was “not impossible but difficult,” he said, while the leak theory was undermined by the fact that the virus was not among those in the lab’s records.

A chance for cooperation

In an ideal world, global powers would come together to uncover the origins of the virus.

The other theories need to be considered, cautiously, too. Even if the virus was not spread as a result of a “gain of function” experiment, its rapid spread raises questions about the risks involved in such experiments.

That’s an issue that wouldn’t just affect China: The United States previously blocked funding to similar experiments amid safety concerns, but resumed it in 2017.

But global efforts to understand the virus have not managed to transcend geopolitics. China has obfuscated international understanding of the virus’s origins. The Associated Press reported last week that although hundreds of thousands of dollars in grants had been given out to those studying the origin of the virus, the publication of any of the findings was being tightly controlled by Chinese President Xi Jinping.

But the Trump administration has not made a cooperative effort on the issue either. Rather than support the effort for an international response to the pandemic, it pulled out of the WHO and escalated tensions with China.

By placing political rivalry above scientific discovery, both China and the United States have undermined research. Some experts think it is now unlikely that the WHO team will have the support to complete a credible investigation.

That would be a massive missed opportunity. As the WHO’s own emergencies chief Mike Ryan said last week, the coronavirus is not the only pandemic humanity will face. “This is not necessarily the big one,” he said.