Scientists from a World Health Organization team investigating the origins of Covid-19 say “the clock is ticking” for their work to continue, amid political controversy and stalemate at a meeting of the UN body’s member states this week. Three members of the WHO-backed team that took part in a scientific mission to China earlier this year have expressed frustration that the next phase of research has yet to begin. “There’s such a huge amount of work we could do, but if we don’t get on with it as quickly as possible we do begin to lose the ability to do follow-up,” British-American disease ecologist Peter Daszak said during the This Week in Virology podcast on Thursday. Daszak was one of over a dozen international experts on the mission examining “phase one” research into how the virus that causes Covid-19 began spreading in Wuhan, where it was first identified in 2019. How the work will continue is up for discussion by health ministers at the World Health Assembly this week. Another team member speaking alongside Daszak, Danish epidemiologist Thea Fischer, pointed to the fanning of a contentious theory that the virus could have escaped from a Wuhan laboratory as one factor slowing the launch of the next phase of work. “I think none of us would ever disagree that this needs to be followed, if somebody has clear leads, it should be shared … but until then let’s keep the focus on the most likely scenarios,” she said. “We are not following all of these [other] leads and recommendations, everything is stalling and this is really devastating.” The team said it was “extremely unlikely” that the virus could have escaped from a laboratory in a joint report with Chinese scientists released after their month-long field mission. It was most likely the virus came from a bat and passed to humans via another animal, they said. But calls from scientists and lawmakers for further investigation of the lab leak theory have been growing within the United States in recent weeks. On Wednesday, US President Joe Biden called for American intelligence to investigate the origins of the virus , including this theory. The move followed media reports of unconfirmed US intelligence that members of the laboratory fell ill in the month before the Wuhan outbreak. Beijing denied the reports and accused the US of “pursuing stigmatisation and political manipulation”. Questions on how the next phase of the research should proceed have hung over the ongoing annual meeting of the WHO’s 194 member countries, the first since the controversial China mission in February. A handful of nations said its conclusions were flawed by a lack of transparency from the Chinese government, a charge Beijing has denied. The US mission to the UN in Geneva on Thursday called “for a timely, transparent, evidence-based, and expert-led phase two study”, including in China, and said they awaited an update from the WHO director general. British ambassador to the UN Simon Manley made similar comments on Thursday. Wuhan laboratory adds another branch to bat coronavirus family tree China’s representative to this week’s health assembly meeting also said Beijing supported further research, but stressed that the “China part” of the work was completed and it was time for other countries to cooperate on global studies into the origins. But the scientists on the mission said additional studies needed to be undertaken in China, as recommended in the joint report agreed on with their Chinese counterparts, who included public health officials and other scientists. “Some of those studies are in China and some of those studies are also outside of China. It’s really a package that needs to be done,” Dutch virologist Marion Koopmans said on Thursday’s podcast. One such recommendation was research into farms that were supplying wild animal products to Wuhan, some of which were located in Chinese provinces where animals with similar viruses to the one that causes Covid-19 had been found. Daszak noted that China had agreed to pursue the recommendations in the report. Fischer also pointed to a “promising” arrangement with a Wuhan blood bank for testing to look for earlier cases of infection. The blood bank had agreed to delay a scheduled, regular destruction of samples after two years in anticipation of further research, Fischer said. However, such samples could be destroyed in other cities that may also have relevant clues. “It’s really like the clock is ticking and we need to move on with these studies,” she said. A WHO spokeswoman told a UN briefing on Friday that the experts would prepare a proposal for the WHO director general, but that there was no set timeline. Earlier this week the WHO’s top emergency expert Mike Ryan said talks with member states about a phase two mission would continue in coming weeks.