The World Health Organization (WHO) has quietly shelved the second phase of its much-anticipated scientific investigation into the origins of the COVID-19 pandemic, citing ongoing challenges over attempts to conduct crucial studies in China, Nature has learned.

Researchers say they are disappointed that the investigation isn’t going ahead, because understanding how the coronavirus SARS-CoV-2 first infected people is important for preventing future outbreaks. But without access to China, there is little that the WHO can do to advance the studies, says Angela Rasmussen, a virologist at the University of Saskatchewan in Saskatoon, Canada. “Their hands are really tied.”

In January 2021, an international team of experts convened by the WHO travelled to Wuhan, China, where the virus that causes COVID-19 was first detected. Together with Chinese researchers, the team reviewed evidence on when and how the virus might have emerged, as part of phase one. The team released a report in March that year outlining four possible scenarios, the most likely being that SARS-CoV-2 spread from bats to people, possibly through an intermediate species. Phase one was designed to lay the groundwork for a second phase of in-depth studies to pin down exactly what happened in China and elsewhere.

But two years since that high-profile trip, the WHO has abandoned its phase-two plans. “There is no phase two,” Maria Van Kerkhove, an epidemiologist at the WHO in Geneva, Switzerland, told Nature. The WHO planned for work to be done in phases, she said, but “that plan has changed”. “The politics across the world of this really hampered progress on understanding the origins,” she said.

Researchers are undertaking some work to pin down a timeline of the virus’s initial spread. This includes efforts to trap bats in regions bordering China in search of viruses closely related to SARS-CoV-2; experimental studies to help narrow down which animals are susceptible to the virus and could be hosts; and testing of archived wastewater and blood samples collected around the world in late 2019 and early 2020. But researchers say that too much time has passed to gather some of the data needed to pinpoint where the virus originated.

Tense times

Many researchers aren’t surprised the WHO’s plans have been thwarted. In early 2020, members of then US president Donald Trump’s administration made unsubstantiated claims that the virus had originated in a Chinese laboratory, and US intelligence officials later said they had begun investigations. The city of Wuhan is home to the Wuhan Institute of Virology, a high-security lab that works on coronaviruses. Chinese officials questioned whether the virus originated inside the country’s borders.

Amid simmering hostility between the two superpowers, WHO member states requested in May 2020 that the agency put together a science-led effort to identify how the pandemic started. Although China agreed to the mission, tensions were high by the time the WHO group left for Wuhan, and engagement with China quickly unravelled after the group returned.

In its March 2021 report, the team concluded that it was “extremely unlikely” that the virus had accidentally escaped from a laboratory. But the inclusion of the lab-incident scenario in the final report was a key point of contention for Chinese researchers and officials, says Dominic Dwyer, a virologist at New South Wales Health Pathology in Sydney, who was a member of the WHO team.

That July, the WHO sent a circular to member states outlining how it planned to advance origins studies. Proposed steps included assessing wild-animal markets in and around Wuhan and the farms that supplied those markets, as well as audits of labs in the area where the first cases were identified.

But Chinese officials rejected the WHO’s plans, taking particular issue with the proposal to investigate lab breaches. Zhao Lijian, the spokesperson for China’s foreign ministry, said the WHO proposal was not agreed by all member states, and that the second phase should not focus on pathways the mission report had already deemed extremely unlikely.

In August 2021, members of the original mission team published a Comment piece in Nature urging quick action on the proposed studies to trace the virus’s origins. “We wrote that piece because we were worried phase two might not happen,” says Marion Koopmans, a virologist at Erasmus University Medical Center in Rotterdam, the Netherlands, and a member of the mission to Wuhan. “I’m sorry to say that that’s indeed what panned out.”

Stalled work

Gerald Keusch, associate director of the National Emerging Infectious Diseases Laboratory Institute at Boston University in Massachusetts, says the origins investigation was “poorly handled by the global community. It was poorly handled by China. It was poorly handled by the WHO.” The WHO should have been relentless in creating a positive working relationship with the Chinese authorities, says Keusch; if it was being stonewalled, it should have been honest about that.

Van Kerkhove says that the WHO’s director-general, Tedros Adhanom Ghebreyesus, has continued to engage directly with Chinese government officials to encourage China to be more open and to share data. And WHO staff have reached out to the China Center for Disease Control and Prevention in Beijing to try to establish collaborations. “We really, really want to be able to work with our colleagues there,” says Van Kerkhove. “It’s really a deep frustration.”

The Chinese ministry of foreign affairs did not respond to Nature’s e-mailed requests for comment on why the phase-two studies have stalled.