The intelligence on the three workers came from outside the United States intelligence agencies’ own collection, which means its veracity is more difficult to authenticate. The source of the information was unclear, but several American officials said they believed the report that the three researchers got sick.
American intelligence officials do not know whether the lab workers contracted Covid-19 or some other disease, like a bad flu. If they did have the coronavirus, the intelligence may suggest that they could have become sick from the lab, but it also could simply mean that the virus was circulating in Wuhan earlier than the Chinese government has acknowledged.
Also toward the end of Mr. Trump’s term, State Department officials began examining the origins of the virus and concluded that it was highly unlikely to have appeared naturally and thus was likely the product of laboratory work.
CNN first reported the effort and suggested that the group’s efforts had been shut down by the Biden administration, prompting scathing Republican criticism. A State Department spokesman, Ned Price, denied that, saying that the team’s findings were briefed to senior officials in the department’s arms control bureau in February and March.
“With the report delivered, the work was ended,” Mr. Price said.
Mr. Trump issued a statement on Tuesday boasting of his early insistence that the Wuhan lab was the source of the virus. “To me, it was obvious from the beginning,” he said. “But I was badly criticized, as usual.”
Despite the absence of new evidence, a number of scientists have lately begun speaking out about the need to remain open to the possibility that the virus had accidentally emerged from a lab, perhaps after it was collected in nature, a lab origin distinct from a creation by scientists.
“It is most likely that this is a virus that arose naturally, but we cannot exclude the possibility of some kind of a lab accident,” Dr. Francis Collins, the director of the National Institutes of Health, told senators on Wednesday.
