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The top U.S. health official spoke out in defense of Obamacare on Wednesday, saying the looming increase in premium costs are a result of insurers initially under-pricing, and not a sign of a broken healthcare system.

Health and Human Services Secretary Sylvia Burwell defended the Affordable Care Act (ACA), popularly known as Obamacare, during a conversation with Washington Post columnist E.J. Dionne Jr. at Georgetown University.

Related: Obamacare Premiums Are Going Up. What Does That Really Mean?

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Burwell said she understands the frustration with the new prices, but insisted that 85 percent of Americans impacted by the increases will be eligible for subsidies so that their coverage remains affordable.

"Whenever we have had major legislation in the United States, you learn and you iterate," Burwell said. "That's an activity that's done with both the Executive Branch and the Legislative Branch working together and that's what I think we're hopeful will happen."

In the early years of health care reform insurers were under-pricing premiums because they did not have access to data, Burwell said. The new increase in costs is a reflection of insurers now being able to adjust prices based on actuarial data, she said.

"I've met the kid who was 15 and had cancer and hit her lifetime limit of insurance," Burwell said. “I’ve met the mother who decided: 'I wasn’t going to get the last chemotherapy treatment until next year because I hit my annual limit.'"

Related: Feds Expect 13.8 Million New Obamacare Customers

Burwell said those families' lives have been changed because of Obamacare, and stressed that she doesn’t see a future where the health system changes to deny those people coverage.

“We’re not going back,” she said. “So, in a world where that is true, the alternative we all have is to work together and improve the things that aren't working well. And I think that's what's going to happen in a new administration."