Biden administration officials are cautioning that a 90-day review into the origins of the Covid-19 virus may not produce a definitive explanation as intelligence agencies take on the challenge of unraveling the global pandemic.

Spy agencies conducting the review have yet to find conclusive evidence that would settle the debate over whether the virus came from human contact with an infected animal or was leaked from a Chinese government virology lab, a person familiar with the efforts said.

President Biden is due to receive a 45-day update in mid-July, and administration officials said that even partial progress might narrow differences among scientists, politicians and intelligence experts and turn up clues for further investigation.

Mr. Biden “is mindful of the fact that after 90 days we may not have an absolutely definitive answer, but he wanted a focused, intense, time-bound effort,” a senior administration official said.

Experts say that knowing the origins of Covid-19 could be important in preparing for future pandemics. The virus has killed more than 600,000 Americans and nearly four million people world-wide, and disrupted the global economy.

Director of National Intelligence Avril Haines said this spring that she has hired more people to work on pandemic threats.

Director of National Intelligence Avril Haines said this spring that she has hired more people to work on pandemic threats.

Photo: jim lo scalzo/EPA/Shutterstock

The review is being overseen by Director of National Intelligence Avril Haines, a lawyer and former deputy director of the Central Intelligence Agency with long ties to Mr. Biden. It requires the vast intelligence community to train its resources on an area it has long treated as far less of a priority than spying on the Russian military, terrorist dangers or China’s weapons buildup: the detection and analysis of global pandemics.

Ms. Haines, who oversees 18 intelligence agencies and has spoken about the need for U.S. intelligence to broaden its work on nontraditional dangers, told lawmakers this spring she had hired additional personnel to work on pandemic threats.

The Covid-19 origins review is an example of the kind of complex, multidisciplinary work spy agencies will increasingly be called on to do on nontraditional threats, said Glenn Gerstell, former general counsel for the National Security Agency, which specializes in electronic eavesdropping. “This is where the intelligence community is going,” he said.

Absent a breakthrough, the review faces many obstacles, chief among them China’s refusal to provide further access to data and scientists from the Wuhan Institute of Virology, a biosecurity lab that has studied coronaviruses. China has said the search should turn to other countries and cited the conclusion of a World Health Organization-led team of experts early this year that a lab leak was “extremely unlikely.”

More than a year into the pandemic, scientists are still debating Covid-19’s origins. WSJ breaks down significant events in three locations in China—a seafood market, a lab and a mine—to piece together how the global health crisis might have started. Photo composite: George Downs The Wall Street Journal Interactive Edition

A daily intelligence briefing Mr. Biden received in the Oval Office in February showed the difficulties the intelligence community has had in identifying the source of the virus. Intelligence officials told Mr. Biden during that session they had numerous questions about the origin of the virus but didn’t have “high confidence” in any particular explanation, more than a year after the virus was first detected in the Chinese city of Wuhan.

Mr. Biden instructed national security adviser Jake Sullivan to follow up, which he did in a meeting with intelligence officials in early March. The White House ordered a written assessment from intelligence officials. Delivered to Mr. Biden in May, the assessment showed one intelligence agency leaning toward the hypothesis that the virus leaked out of a lab and two intelligence agencies leaning toward the view that it arose naturally—all with low or moderate confidence. Most agencies said there wasn’t enough evidence to render a judgment.

That inconclusive assessment and China’s statement to the WHO that it considered the Covid-19 origins investigation in its country to be complete, led to Mr. Biden’s order to mount what a senior administration official called an “all hands on deck effort” over a 90-day period.

Within Ms. Haines’s office, officials said, the review is being coordinated by the National Counterproliferation Center, which oversees intelligence efforts to combat nuclear, chemical and biological proliferation.

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The National Security Agency, the officials said, will look for clues in its vast stores of intercepted foreign electronic communications, most of which aren’t analyzed in real time. The effort is being aided by experts from government labs, the Centers for Disease Control and Prevention, the National Institutes of Health and other parts of the Department of Health and Human Services. Experts outside the government are being consulted, as are allied intelligence agencies.

One outcome, Mr. Biden said in a May statement when he announced the review, could be a list of specific questions that the U.S. would put to China as well as recommendations on what additional inquiries might be needed.

Given the possibility that the intelligence review might be inconclusive, there are already calls by leading lawmakers, some experts outside government and a grass-roots group of people affected by Covid-19 for an independent national commission.

“There has not yet been a properly organized, independent, scientific evaluation of all of the available evidence,” said Philip Zelikow, the former executive director of the commission on the Sept. 11 terrorist attacks. Mr. Zelikow is heading a planning group, backed by prominent foundations, for a possible commission to investigate how Covid-19 emerged and how to better prepare for future pandemics.

Memorials at a New York City cemetery this month remembered the lives of those killed by the Covid-19 pandemic.

Memorials at a New York City cemetery this month remembered the lives of those killed by the Covid-19 pandemic.

Photo: Spencer Platt/Getty Images

The Trump administration didn’t organize an intensive governmentwide review into Covid-19’s origins, though intelligence agencies and the Lawrence Livermore National Laboratory probed the matter, former Trump administration officials said.

State Department officials also used the authorities of the arms-control bureau, which has the mission of assessing compliance with the biological-weapons convention and other arms-control accords, to request intelligence reports on Covid-19’s origins.

In a fact sheet that was vetted by the Office of the Director of National Intelligence and released publicly on Jan. 15, the State Department reported that several researchers at the Wuhan Institute of Virology had become ill during the fall of 2019 with symptoms that were consistent with Covid-19 or a seasonal flu. The fact sheet also said there were links between the lab and the Chinese military, though it also noted that the U.S. government hasn’t determined how the virus began. Biden officials haven’t challenged or amended those statements.

Andrew Weber, a consultant to the Lawrence Livermore lab and a former senior Pentagon official who worked on biological defense programs, said the broad scope and focus of the Biden effort could yield important information.

“It is very rare to do such a high-level and intensive deep dive,” Mr. Weber said.

Still, the longer time elapses from the initial outbreak the more difficult it becomes to trace its origins, especially without more access from China, according to some experts and former officials.

The inability of the U.S. government to access the Wuhan lab and its employees “will make it very difficult at the end of the day to get to the goal line,” said William Evanina, who was U.S. counterintelligence chief for nearly six years until January.

Write to Michael R. Gordon at michael.gordon@wsj.com and Warren P. Strobel at Warren.Strobel@wsj.com