Pandemic's Origins Still a Mystery As Scientists Question Bizarre 'Frozen Food' Theory

More than a year into a global pandemic, after SARS-CoV-2 has killed more than two million people and infected more than 100 million, China finally allowed a team of international experts, under the auspices of the World Health Organization, into the country to investigate the origins of the deadly coronavirus. The team's conclusions raised new questions and did nothing to bridge the divide between China and the West.

The 10 scientists on the WHO team worked with Chinese officials and scientists online while quarantined for two weeks, and then spent another two weeks visiting sites in Wuhan, where the first outbreak occurred. They held a briefing before heading to the airport, offering two notable messages. They dismissed the "lab-leak hypothesis"—the theory that the coronavirus emerged from a lab accident—saying it was "extremely unlikely" and warranted no further investigation. And they elevated an alternate theory that scientists had previously discounted: that the coronavirus may have arrived in Wuhan hidden in frozen food imported from elsewhere.

 Institute of Virology in Wuhan
Security personnel stand guard outside the Wuhan Institute of Virology in Wuhan as members of the World Health Organization (WHO) team investigating the origins of the COVID-19 coronavirus make a visit to the institute in Wuhan in China's central Hubei province on February 3, 2021. HECTOR RETAMAL/AFP/Getty

The frozen-food theory was surprising. The scientists say they saw no direct evidence that such transmission actually occurred; they based their recommendation on reports that carcasses of wild animals had been present in the Wuhan wet market, only a few blocks from the Wuhan Institute of Virology, when the first outbreaks occurred. Some mammals, such as ferret-badgers, are known to be potential carriers of coronaviruses. When Chinese scientists tested the carcasses in January 2020, they found no evidence of SARS-CoV-2.

Nevertheless, the team said the possibility was worthy of further investigation. "Scientists tested those carcasses and they were negative, and that's good," Peter Daszak, president of EcoHealth Alliance, a research firm, and a member of the delegation, told CNN. "But we don't know what else was there. We don't really know if there were live animals there—there's no evidence of that, but we don't know. And we don't know how many of these animals were part of this frozen market or even other types of meat. To many of us on the team, it was a clear clue as to what may have happened, and it was one of the pathways that we thought were more likely than others, for sure."

Scientists have not paid much attention to the frozen-food hypothesis in part because there is little evidence that such transmission has occurred. One study with a positive result was published in December in the journal Biosafety Health. During an outbreak in the Chinese city of Qingdao, scientists found SARS-CoV-2 on the outer packaging of frozen cod and concluded that "the COVID-19 outbreak of Qingdao was probably caused by SARS-CoV-2 contamination of cod outer package during production or cold-chain transportation." In other words, the medium of transmission was the packaging rather than the food itself.

"The probable source of this cluster was determined to be two dock workers from the city's port," the authors wrote, "who were determined on September 24 to have asymptomatic infection. They had no history of travel or contact with anyone confirmed to have Covid-19, but they may have contracted the virus from ship workers or contaminated cargo."

The conclusion is consistent with Beijing's insistence in recent months that several major outbreaks were triggered by frozen-food imports. Officials point to traces of the virus found on packages of pork, shrimp and beef and instituted mandatory testing of foreign imports, the Wall Street Journal reported in December.

It's not consistent with other evidence, however. In the early months of the pandemic, studies showed that transmission of the coronavirus by food, frozen or otherwise, is negligible, especially when compared to airborne transmission. Since then, "nothing has changed," said Martin Wiedmann, a food safety expert at Cornell University, at an online briefing, in response to a question about the WHO briefing. "There is no reason to test foods, the risk is infinitesimally small, so essentially zero."

"Simply finding the presence of genetic material on the surface of frozen food just doesn't fit the transmission model from what we know of millions and millions of cases," says Ruth Petran, a food-safety expert. "We know it's primarily through droplets containing infectious virus particles spread from one infected person to another." To conclude that dock workers in Qingdao got COVID-19 from handling cod "would be like saying that Uber drivers are getting infected by touching the seat belts in their cars," tweeted Alina Chan, a molecular biologist at the Broad Institute and a vocal advocate for further investigation of the lab-leak hypothesis.

Shi Zhengli
Shi Zhengli, director of the Center for Emerging Infectious Diseases at the Wuhan Institute of Virology. Shi has said no one at the institute has been infected with SARS-CoV-2. JOHANNES EISELE/AFP via Getty Images

The discrepancy between the WHO and the scientific consensus on frozen-food transmission comes down to politics, says Wiedmann. "We tend to think of the WHO as an impartial science-based organization," he says. "But it is also a global organization that needs to work in partnership with multiple countries, with potentially differing interpretations of the data or different risk perceptions.

"They can't go into a country and say, 'this theory about frozen foods is hogwash' or they'd destroy any collaborations that are needed going forward."

The group's dismissal of the lab-leak hypothesis was less surprising. Most scientists believe that a lab origin is less likely than a natural one, and China has vigorously denied the possibility. So has Daszak. Because he has worked closely with scientists at WIV on bat coronaviruses and provided funding through contracts with the National Institutes of Health, he recused himself from deliberations regarding a possible lab leak.

Still, in Wuhan, he responded to a BBC reporter's question about how the group reached its conclusion. "A very large group of experts have looked at this," he said. "They've been to the various labs around the region, and talked to people, asked critical questions, got critical answers, and they've come to their conclusion, and I have as well. What they say is 'extremely unlikely,' and that stands alone."

The team's press briefing failed to persuade U.S. officials. When asked about the recommendations at a briefing on February 9, State Department spokesperson Ned Price said: "We look forward to receiving the report and the data from the WHO investigation." He referred reporters to a State Department fact sheet from Jan 15, which says, "We have not determined whether the outbreak began through contact with infected animals or was the result of an accident at a laboratory in Wuhan, China."

Before it discounts the lab-leak theory, the State Department wants to see:

  • An investigation of illnesses that may have arisen among staff at WIV in the months prior to the pandemic, including interviews with researchers who were ill;
  • Records on WIV's work on bat coronaviruses before the pandemic, including experiments involving RaTG13, the closest known virus to SARS-CoV-2, and any "gain-of-function" research; and
  • Information on any U.S. funds that were used on military bioweapons research at WIV. The U.S. claims Beijing has carried out military experiments on laboratory animals since 2017.

Unless the final WHO report contains this kind of evidence, calls for more transparency will continue and the origins of the virus will remain a mystery. That may be good for Chinese officials but it's dangerous for everyone else.