The C.I.A. has said for years that it did not have enough information to conclude whether the Covid pandemic emerged naturally from a wet market in Wuhan, China, or from an accidental leak at a research lab there.

But the agency issued a new assessment this week, with analysts saying they now favor the lab theory.

That shift is based on “the available body of reporting,” although the other theory remains plausible, a spokeswoman for the agency said, adding that the agency will continue to evaluate any available credible new intelligence reporting.

Some American officials say the debate matters little: The Chinese government failed to either regulate its markets or oversee its labs. But others argue it is an important intelligence and scientific question.

John Ratcliffe, the new director of the C.I.A., has long favored the lab leak hypothesis. He has said it is a critical piece of intelligence that needs to be understood and that it has consequences for U.S.-Chinese relations.

The announcement of the shift came shortly after Mr. Ratcliffe told Breitbart News he no longer wanted the agency “on the sidelines” of the debate over the origins of the Covid pandemic. Mr. Ratcliffe has long said he believes that the virus most likely emerged from the Wuhan Institute of Virology.