Kathleen Sebelius, secretary of the U.S. Department of Health and Human Services (HHS), has resigned, Kaiser Health News reports. President Barack Obama has nominated Sylvia Mathews Burwell, director of the Office of Management and Budget (OMB), to replace Sebelius, a former Kansas governor and insurance commissioner.

The resignation by Sebelius comes after she presided over the troubled rollout last October of HealthCare.gov, which was hampered by technological problems that prevented sign-ups. She successfully managed fixes to the site, which have led to 7.5 million people enrolling in health plans under the Affordable Care Act (ACA).

In her role at OMB, Burwell helped the Obama administration get through the shutdown of the federal government last October. She served in the Clinton administration and worked for the Bill & Melinda Gates Foundation. Burwell also was president of the Walmart Foundation.

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