The WHO also lacks the authority to march into a country to investigate health conditions; it needs to be invited.

“We’ve seen both China and the US react to this pandemic through the lens of geopolitics and that’s been very, very disruptive,” said David Fidler, a legal scholar and adjunct senior fellow with the non-profit Council on Foreign Relations in New York. That was making it difficult to even agree on what an investigation into the outbreak would focus on, he said.

“No one was concerned about how Sars was going to affect the distribution of power in the international system,” said Fidler, who advised the WHO on rewriting its International Health Regulations after Sars. The rules were changed to promote transparent reporting of outbreaks and to help combat the growing threat from the cross-border spread of diseases. In all, 196 countries signed on to the IHR standards.

Robert Breiman had a front-row seat to the response to Sars, or severe acute respiratory syndrome, in 2003. The epidemiologist was pulled from his work on infectious disease in Bangladesh to lead WHO investigative teams in China at the time.

“It was a very very different time than what we’re in right now in that everybody was united around figuring out what this was and finding the best ways to prevent illness,” said Breiman, also a former official at the US CDC. “There was no political side at all.”

But Covid-19 appeared amid acrimonious relations and mistrust between the US and China, following an 18-month trade war, recriminations over civil liberties, and conflicts about Beijing’s claims to areas of the South China Sea – to mention just a few areas of friction. The pandemic just made it worse.

“The rhetoric, the escalating accusations, the conspiracy theories – it’s a spiral of adverse effects,” Fidler said.

In 2003, researchers from the University of Hong Kong were the first to trace the Sars infection to similar wet markets in Guangdong province in southern China, concluding that civet cats sold in the markets were the likely intermediate host.

The university’s Dr Leo Poon Lit-man, one of the first researchers to decode the Sars genetic sequence and develop diagnostic tests, explained why it was important to trace and understand the origin of pathogens.

“By understanding the transmission routes, we may develop control measures,” he said. “There could be several dozens of that type of virus circulating in China. Also, there are similar viruses in the region. Could it happen again? How could it happen?”

The WHO has said that China’s scientists are investigating the origins of Covid-19. This includes environmental sampling at markets and farms in areas where the first human cases were identified and tracing the source and type of wildlife species and farmed animals sold in wet markets.

Poon, who is not involved in the Covid-19 investigation, said researchers would need to trace where any infected animal came from. It could have been shipped to Wuhan from elsewhere in China or other parts of the world, he said.

“My gut feeling is the wet market played a role, like what you had for Sars. But now, we don’t have evidence, it is still speculation,” he said.

Meanwhile, more than four months have passed since China alerted the WHO about the outbreak. China has said it collected hundreds of samples from the Wuhan market, including dozens with the virus, but it has not publicly shared further details. There is still no clarity on any intermediate animal or how the virus got into humans.

In that time, millions of people have been infected, many millions more have lost their livelihoods as lockdowns to stop the spread of the disease have shut down businesses around the world. Governments are spending trillions of dollars on bailouts and world leaders want answers about the origin of Covid-19 to prevent it from happening again.

As part of those demands, the European Union will co-sponsor a resolution for an “independent review” of the international health response to Covid-19 when the World Health Assembly convenes for a virtual meeting on May 18.

The WHO last week said it was in talks with China to investigate the origin of the virus, following up on a week-long joint mission in February. China so far has not agreed to any international investigations, stating only that it supports a WHO-led global review of the outbreak at an “appropriate time after the pandemic is over”.

“What we object to is the attempt to politicise the tracing of origin of the virus by the US and some other countries, who are so eager to launch an international inquiry based on the presumption of guilt,” Chinese foreign ministry spokeswoman Hua Chunying said last week.

The WHO has also been dogged by criticism that it pandered to Beijing in its handling of Covid-19 information.

The Trump administration last month said it would suspend funding to the health body to investigate the WHO’s relations with China. This raises doubts about whether Washington would accept the results of any WHO-led investigation into Covid-19.

All of which highlight the structural flaws in the global health system for dealing with epidemics and the International Health Regulations introduced after Sars.

“IHR essentially mandates that outbreaks of potential international importance should be investigated with whatever it takes, as early as possible, and that should include when needed, [the] WHO,” said Breiman, now a professor of global health at Emory University’s Rollins School of Public Health in Atlanta.

The rules also required complete transparency about the scope of the outbreak, he said. “That’s sometimes where the IHR breaks down, because there’s no enforcement capability.”

Antoine Flahault, director of the Institute of Global Health at the University of Geneva, stressed that whether countries ask the WHO to work with them to combat a disease on the ground comes back to their own capacity and inclination.

If a country had the means “usually it does not accept any intrusion in their territories and they want to take the lead on such missions”, Flahault said.

But in the case of China, the issue was more than just scientific know-how, said Sara Davies, a global health governance expert and professor of international relations at Australia’s Griffith University.

“China is not a democracy with an open, free and fair press and with groups of scientists who work independent to the government, and so it creates a constant undercurrent of mistrust about the information that comes out,” Davies said.

Yanzhong Huang, a senior fellow for global health also at the Council on Foreign Relations, said he thought the WHO and China would reach an agreement about a joint mission to investigate the virus’s origins. Though, the question remains: would its findings be accepted?

“The key issue is who will be included in this investigation and which places will they be allowed to visit,” Huang said. If they did not get access to the Wuhan lab that some US politicians have linked to the pandemic then those individuals would question the credibility of the assessment, he said.

But no investigation at all runs a higher risk. “If you don’t know the origin, the animal could continue to shed the virus, and you are never going to stop it,” he said.

Politics aside, Poon at HKU said international collaboration on research into the coronavirus was essential because the virus itself knew no borders.

As a public health scientist, his role was to find out the facts to prevent other epidemics, he said. “What we want to know is the truth.”