The C.D.C.’s ex-director offers no evidence in favoring speculation that the coronavirus originated in a lab.

The former director of the Centers for Disease Control and Prevention said in a CNN clip on Friday that he favored a theory, decried by many scientists and rejected as “extremely unlikely” by at least one World Health Organization international expert, that the coronavirus escaped from a lab in Wuhan. The former official, Dr. Robert Redfield, offered no evidence and emphasized that it was his opinion.

“I am of the point of view that I still think the most likely etiology of this pathogen in Wuhan was from a laboratory,...