On Thursday, the Trump administration selected Jim O’Neill, a former biotechnology executive and the deputy to Health Secretary Robert F. Kennedy Jr., to serve as the acting director of the Centers for Disease Control and Prevention.

The pick leaves the nation’s premier public health agency under the leadership of an official without medical or scientific training and seems likely to tighten political control of the agency.

The decision follows a tumultuous few days at the agency in which its new director, Susan Monarez, was fired and several other top officials resigned. The departures were driven by deep disagreement over vaccine policy.

Mr. Kennedy, a longtime vaccine critic, is seeking to transform the nation’s vaccine policy; under his leadership, officials have already limited eligibility for Covid-19 vaccines.

In an email sent to C.D.C. staff on Thursday night, Mr. Kennedy said that he was “committed to working with you to restore trust, transparency and credibility” to the agency. Tapping Mr. O’Neill as acting director would “help advance this mission,” he added.

Mr. O’Neill was confirmed as the deputy secretary of health and human services in June. It was a return to the federal government for Mr. O’Neill, who also worked for the department from 2002 to 2008, under President George W. Bush.