China’s rebuff of the World Health Organization’s planned second phase investigation into the origins of Covid-19 highlights the difficulty it faces in operating amid political pressure from its most powerful members.

WHO chief Tedros Adhanom Ghebreyesus last week announced five priorities for further research — but by far the most controversial was the last item on his list: “Audits of relevant laboratories and research institutions operating in the area of the initial human cases identified in December 2019”.

This proposal to investigate the “lab leak” hypothesis – that the virus may have escaped from a laboratory in Wuhan – prompted a flat-out rejection from China.

On Thursday, Zeng Yixin, the health vice-minister, described it as “disrespectful to common sense and contrary to science”. Zeng also said that the WHO had veered too far from the recommendations made after a mission to China earlier this year, which said the lab leak theory was highly unlikely and did not warrant further investigation.

However, the US and other countries have criticised that mission for being incomplete and compromised, with some researchers warning that the scientists had lacked access to key information such as hospital data, a realistic picture of the city’s wildlife trade and details of the viruses stored in Wuhan’s laboratories.

Tedros last week said the mission had faced a “challenge” in getting access to raw data and called on China to be “transparent, open and cooperate”. He also urged all WHO members to avoid “politicising” the scientific process.

The comments were the most public condemnation of a member state made by a director general since Gro Harlem Brundtland criticised China during the severe acute respiratory syndrome outbreak in 2003, according to Lawrence Gostin, director of the WHO Collaborating Centre on Public Health Law & Human Rights at Georgetown University in the US.

“Clearly China has pushed him past his point of patience, and also he’s under a great deal of pressure from the West and there’s an election looming, so you’ve got three huge factors that have influenced his behaviour,” he said, referring to next year’s vote to select the next WHO director general.

The WHO and its director general’s relationship with China have come under scrutiny during the pandemic.

Former US president Donald Trump hit out at Tedros for praising China’s early response and moved to cut ties with the agency, which he called a “puppet of China” – a decision Joe Biden later reversed.

More recently, the US, Britain, Japan and others have suggested the first mission into the origins was subject to “undue influence” from China and have been clamouring for a “transparent” second phase. China has defended its transparency and cited patient confidentiality when it comes to sharing raw data.

The WHO is currently consulting member states on its plans to continue the investigation but Thursday’s rebuff highlights the constraints placed on it by its members, especially since it cannot conduct research in countries without their permission.

“All eyes are on China now as the conclusion of this inquiry depends on China’s cooperation and transparency,” said Ayelet Berman, lead in global health at the Centre for International Law at the National University of Singapore. “It is a known fact that the WHO has no enforcement powers.”

Gostin said a rebuff from China could also feed into “stereotypes that the WHO is a paper tiger” with no influence and authority.

“This is quite fundamental, we are talking now about how did it all begin, and if you can’t even know how it began, how can you claim to have managed the pandemic well?” he said.

Zeng’s rejection of the WHO proposal also stressed the need for “multi-country” research to explore if the virus began overseas.

But aside from the call for more research into animal markets in Wuhan, the outline proposal did not limit the research to specific geographic areas, leaving open the option of broader studies as recommended in the phase one report.

Wang Yiwei, director of the institute of international affairs at Renmin University of China, said political influence from the United States was probably why the WHO had called for further research into the lab leak theory.

“The US wants to use China as a target … and damage China’s reputation … so again and again they want to find the origin [of the virus] in the Wuhan laboratory, even though of course they cannot find any evidence there,” he said.

There is currently no public evidence that any facility in Wuhan had a virus close enough to the Covid-19 virus to have caused the outbreak, but a number of scientists have said the meeting between officials at the Wuhan Institute of Virology – which had been studying coronaviruses in bats – and the WHO-led team was not enough to exclude the theory.

Gerald Keusch, associate director of the National Emerging Infectious Diseases Laboratory Institute at Boston University, was one of the signatories of a recent letter to The Lancet medical journal that said natural origin was the option supported by credible, existing evidence.

He said the lab leak theory still warranted investigation, even if it was a lower priority, but he worried that the rhetoric surrounding it could make it hard to move forward research in China.

“All of the accusatory statements and hypotheses built on no publicly available evidence will not gain access to an open, clear, transparent, collaborative international investigation,” he said.

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