The Biden administration renewed its appeals this week for a more rigorous investigation into the origins of the coronavirus as the World Health Organization faced mounting criticism for an earlier report dismissing the possibility that it had accidentally escaped from a Chinese laboratory.
The calls from top American health officials this week were the latest in a series of White House demands in recent months that any such inquiry be free from Chinese interference. But they drew additional attention as some scientists have expressed a new openness to the idea of a lab accident and the W.H.O. grappled with how to respond.
Xavier Becerra, the U.S. health and human services secretary, said at an annual meeting of the W.H.O. on Tuesday that preparing for the next pandemic required a fuller study of the origins of this one.
“Phase two of the Covid origins study must be launched with terms of reference that are transparent, science-based and give international experts the independence to fully assess the source of the virus and the early days of the outbreak,” Mr. Becerra said.
Andy Slavitt, one of President Biden’s top coronavirus advisers, was more pointed in his criticisms of the W.H.O. and China. A joint W.H.O.-China inquiry whose findings were released in March dismissed as “extremely unlikely” the possibility that the virus had emerged accidentally from a laboratory.
“We need to get to the bottom of this and we need a completely transparent process from China,” Mr. Slavitt told reporters on Tuesday. “We need the W.H.O. to assist in that matter. We don’t feel like we have that now.”
Suggestions that the coronavirus may have been accidentally carried out of a laboratory in late 2019 in the Chinese city of Wuhan were largely drowned out last year by scientists’ accounts of its likely path from an animal host to humans in a natural setting.
Many scientists believe that a so-called spillover event remains the most plausible explanation for the pandemic. But the joint inquiry by the W.H.O. and China did not settle the matter: The Chinese government repeatedly tried to bend the investigation to its advantage, and Chinese scientists supplied all the research data used in the final report.
In early March, a small group of scientists calling themselves the Paris group released an open letter calling for an inquiry separate from the team of independent experts sent to China as part of the W.H.O. investigation.
This month, a group of 18 scientists said in a letter published in the journal Science that there was not enough evidence to decide whether a natural origin or an accidental laboratory leak caused the Covid-19 pandemic.
After the findings of the joint inquiry by China and the W.H.O. were released in March, the director of the W.H.O., Dr. Tedros Adhanom Ghebreyesus, conceded that the lab leak theory required further study, saying he did not believe that “this assessment was extensive enough.”
And countries including Australia, Germany and Japan have continued at this week’s W.H.O. meeting to call for firmer steps toward a more comprehensive investigation.