Centene Corp. Chairman and CEO Michael Neidorff is taking a medical leave of absence effective immediately, the insurer said Thursday.

St. Louis-based Centene named James Dallas as acting chairman in Neidorff’s stead, while its day-to-day management will be led by vice chairman of the board Sarah London, president and chief operating officer Brent Layton, chief financial officer Drew Asher and chief administrative officer Shannon Bagley. The health system is hoping to hire Neidorff’s replacement by the end of the second quarter.

“I have full faith and confidence in this leadership team and their ability to execute on Centene’s value creation strategy,” Neidorff said in a news release. “As I deal with a treatable medical condition, I want to thank the team for their ongoing work and dedication to lead this exceptional company.”

Neidorff plans to retire in 2022 as part of a leadership shakeup at Centene announced in December. He has served as chief executive for 26 years, first joining in 1996. He has one of the highest compensation packagesat $25 million, among insurer executives.

Politan Capital Managementwhich acquired a $900 million stake in the company last year, gained partial authority over the board’s makeup. The insurer and the hedge fund have entered into a formal cooperation agreement, Centene said when it announced Neidorff’s planned retirement.

Neidorff has been named one of Modern Healthcare’s 100 Most Influential People in Healthcare for several years.