WASHINGTON -- President Barack Obama announced Thursday that 8 million people had signed up for health insurance under the Affordable Care Act, and that 35 percent of them were under age 35, countering those who predicted that it would attract mainly older and sicker people.
The final number exceeds by 1 million the target set by the administration for people to buy insurance through government-run health care exchanges. In particular, the number of young people signing up appears to have surged during the final weeks of enrollment.
"This thing is working," Mr. Obama said. "The Affordable Care Act is covering more people at less cost than most people would have predicted a few months ago."
The president's remarks, delivered in the White House briefing room, amounted to a second victory lap after he announced two weeks ago that 7.1 million people had signed up for insurance during the initial enrollment period, which ended in March. The administration extended the sign-up period by two weeks, until Tuesday, to accommodate late applicants, and the new numbers suggested that interest was running high.
While the number of younger applicants has risen, it remains below the level some analysts believe is needed for the long-term viability of the insurance marketplace. The administration said 28 percent of those who bought policies were between ages 18 and 34; some analysts said the optimum level would be 40 percent.
Still, after a disastrous rollout due to a glitch-ridden government website, and the melancholy announcement last week that Health and Human Services Secretary Kathleen Sebelius would resign, Thursday's announcement was further evidence that the president's signature legislative initiative is enjoying a dramatic reversal of fortune.
Mr. Obama seized on the numbers to make his case that the law is a success, to challenge Republicans to drop their opposition to it and push states that have chosen not to implement it. "I find it strange that the Republican position on this law is still stuck," he said. "They still can't bring themselves to admit that the Affordable Care Act is working."
Mr. Obama spoke after meeting with state insurance commissioners at the White House, in which he shared some of the new enrollment numbers and demographic data.
Critics of the law have cautioned that promising top-line numbers were not by themselves proof of success. In addition to the demographic composition of the people who buy insurance, the number of those who were previously uninsured is important, since many could simply have been moved from plans that were canceled by the law.
White House officials did not say how many of the 8 million people were switching from insurance they had before. Officials have promised to release that information when they have it, but have said it is not data that is collected by the government. Administration officials have also not said how many people have made their first premium payments. Critics have said many of those who signed up have not yet paid.
"All told, millions of Americans who were uninsured have gained coverage," Mr. Obama said. "We've got a sizable part of the U.S. population, for the first time, that are in a position to enjoy the financial security of health insurance."
In the early months of sign-ups, the percentage of people between ages 18 and 34 -- who tend to be healthier -- hovered around 25 percent. But as White House officials had predicted, many appear to have waited until close to the March 31 deadline to enroll, increasing their participation.
Health experts have long warned that the state-by-state, competitive insurance marketplaces set up by the law could be severely undermined if the pool of customers who signed up were mostly sick or elderly. If that were the case, premiums could spike, and insurance companies could choose to abandon the federal marketplaces entirely.
The overall percentage of young people enrolled is not a guarantee that all of the insurance marketplaces across the nation will work perfectly. Individual insurance firms will make decisions about what their premiums will be, based on the makeup of their own client list.
But the higher proportion of young enrollees is a strong rebuke to Affordable Care Act critics, who had predicted that it would fail to attract younger, healthier insurance customers.
In the months ahead, insurance companies will assess the age and health of their customers as a way of determining their premiums for next year. Mr. Obama said he expected that premiums will probably rise, as they have annually for many years.