David Jackson and Kelly Kennedy

USA TODAY

WASHINGTON — President Obama said Thursday that a total of 8 million people signed up for health insurance under the Affordable Care Act during the initial enrollment period that ended March 31.

"The Affordable Care Act is now covering more people at less cost than most would have predicted just a few months ago," Obama said during a White House news conference.

The rise in health care costs is slowing and previously uninsured Americans are now covered, Obama said, adding: "This thing is working."

Obama again criticized Republicans who want to repeal the law, saying it's time to "move on" and focus on jobs and the overall economy. He called for "a change in attitude on the part of the Republicans."

Congressional Republicans continued to criticize the law, questioning the significance of some of the statistics and saying it will lead to higher costs and worse health care for most Americans.

"I have a question," tweeted House Majority Leader Eric Cantor, R-Va. "How many Obamacare enrollees were previously uninsured?"

Senate Minority Leader Mitch McConnell, R-Ky., cited the number of people who saw previous policies canceled: "Noticeably absent from the president's remarks today was any mention of the millions of Americans who were deceived about what Obamacare would mean for them and their families."

Opponents of the law say they're still waiting to hear how many people pay for their policies, if enough healthy people have enrolled to make the exchanges financially workable in the future and how many of the enrollees use a month's worth of benefits to cover medical procedures they couldn't afford before but then discontinue paying for their insurance.

Obama spoke shortly after meeting with a group of state insurance commissioners, some of whom reported that the president cited a rush of young people — under age 35 — signing up late.

In the state-based insurance exchanges, 28% of new enrollees were ages 18 to 34, the Department of Health and Human Services reported Thursday. The department also touted the 3 million adults younger than 26 who are insured through their parents' plans, and 3 million people enrolled in Medicaid and the Children's Health Insurance Plan program as of February.

The news follows a busy week on the health care front.

Health and Human Services Secretary Kathleen Sebelius announced last Thursday she would step down from her post, the same day she told the House Finance Committee that the exchanges had enrolled at least 7.5 million people — 1.5 million more than the Congressional Budget Office projected in February, and half a million more than the office originally projected last year.

Obama has nominated Sylvia Mathews Burwell, current director of the Office of Management and Budget, to replace Sebelius at HHS.

On Monday, CBO reported that it expects as many as 5 million people a year to get health insurance directly through private insurers. That's in addition to the 8 million Obama said have now signed up through the ACA exchanges.