WASHINGTON, April 11 -- U.S. President Barack Obama on Friday nominated a new department secretary to lead the federal health reform programs, accepting resignation of his Health and Human Services Secretary Kathleen Sebelius.

Sebelius announced her resignation just about two weeks after the ObamaCare enrollment period drew to a close on March 31, which attracted more than 7 million people signing up under the Affordable Care Act exchanges.

Sebelius, having served five years with the president, was among the longest-serving Cabinet secretaries in the administration.

Obama nominated the White House budget office director Sylvia Matthews Burwell to replace her.

Obama, speaking in the Rose Garden of the White House, thanked Sebelius for her "extraordinary service" and said that despite the rocky rollout, Sebelius' team "turned the corner, got it fixed, got the job done, and the final score speaks for itself."

"In early March, Sebelius told me she'd be moving on once the first open enrollment period under the Affordable Care Act came to an end," Obama said.

In her farewell remarks, Sebelius said they were "on the front lines of a long overdue national change."

"If confirmed by the Senate, I look forward to carrying on the important work of ensuring that children, families, and seniors have the building blocks of healthy and productive lives, whether it's through implementing the Affordable Care Act, supporting affordable childcare, or finding new frontiers to prevent and treat disease," Burwell said.

The Harvard-educated Burwell was confirmed as White House budget director last April, and previously worked at the top levels of major foundations, including as president of the Walmart Foundation.