“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.
Some scientists attributed the shift in part to the fact that the more extreme proponents of a lab leak hypothesis, like Mr. Navarro, had drowned out the more measured discussions of how lab workers could have accidentally carried the virus outside.
Scientists had been reluctant to discuss the lab leak hypothesis last year because they had been on guard against disinformation, said Marc Lipsitch, a Harvard epidemiologist.
“Nobody wants to succumb to conspiracy theories,” he said.
But the March report by the group of W.H.O.-chosen experts in collaboration with Chinese scientists, dismissing the possibility of a lab leak as “extremely unlikely,” compelled some scientists to speak out.
“When I read that, I was very frustrated,” said Akiko Iwasaki, an immunologist at Yale University. Along with Professor Lipsitch, she signed a letter published in the journal Science this month saying that there was not enough evidence to decide whether a natural origin or an accidental laboratory leak caused the coronavirus pandemic.