(Reuters) - The U.S. Food and Drug Administration said on Tuesday it had named Scott Steele as acting director of its Center for Biologics Evaluation and Research (CBER), following the exit of top vaccine scientist Peter Marks.

An FDA insider for the past five years, Steele has advised on medical policy and served as senior adviser at CBER. He was an adviser on science and technology at the White House during George W. Bush’s administration.

Marks, who played a key role in U.S. President Donald Trump’s first term in developing COVID-19 vaccines, was forced to resign, a media report said, leading to a selloff in drugmakers’ stock on Monday.

His resignation is the highest-profile exit at the regulator amid the Trump administration’s overhaul.

US Health Secretary Robert F. Kennedy, a well-known vaccine skeptic, last week announced plans to reshape federal public health agencies, including cutting jobs of 10,000 employees and centralizing some functions of the FDA, CDC and others under his purview.

The administration began the layoffs on Tuesday, according to multiple sources familiar with the situation, with security guards barring entry to some employees just hours after they received dismissal notices.

Marks will leave effective April 5, according to his resignation letter, the Wall Street Journal said on Friday. He criticized Kennedy’s views on vaccines in the letter.