The figures tell only part of the story. The administration has yet to provide a December update on the 14 states running their own exchanges. While California, New York, Washington, Kentucky and Connecticut have performed well, others are still struggling.
Still, the end-of-year surge suggests that with HealthCare.Gov now functioning better, the federal market may be starting to pull its weight. The windfall comes at a critical moment for Obama's sweeping health care law, which becomes "real" for many Americans on Jan. 1 when coverage through the exchanges and key patient protections kick in.
"As we continue our open enrollment campaign, we experienced a welcome surge in enrollment as millions of Americans seek access to affordable health care coverage," Marilyn Tavenner, the head of the Center for Medicare and Medicaid Services, said in a blog post.
The fledgling exchanges are still likely to fall short of the government's own targets for 2013. That's a cause for concern, because Obama needs millions of mostly younger, healthy Americans to sign up to keep costs low for everyone. The administration had projected more than 3.3 million overall would be enrolled through federal and state exchanges by the end of the year.
Tavenner said fixes to the website, which underwent a major overhaul to address widespread outages and glitches, contributed to December's figures. But the problems haven't totally disappeared. Thousands of people wound up waiting on hold for telephone help on Christmas Eve for a multitude of reasons, including technical difficulties.
The administration released the figures Sunday while President Barack Obama was vacationing in Hawaii. Although the president has spent most of his time relaxing with friends and family, he stepped into work mode late Friday for an update from aides on his signature domestic policy achievement. The White House said Obama told his team to focus on minimizing disruptions for those switching plans.
For Americans who successfully chose insurance plans by Dec. 24, coverage should start on New Year's Day for those who pay their first month's premium by the due date, which in most cases has been extended until Jan. 10.
But insurers have complained that another set of technical problems, largely hidden from consumers, has resulted in the government passing along inaccurate data on enrollees. The White House says the error rate has been significantly reduced. Yet with a flood of signups that must be processed in just days, it remains unclear whether last-minute enrollees will encounter a seamless experience if they try to use their new benefits come Jan. 1.
The political fallout from the website's calamitous rollout could pale in comparison to the heat that Obama might take if Americans who signed up and paid their premiums arrive at the pharmacy or the emergency room and find there's no record of their coverage. Republican critics, already on the lookout for health-law failures to exploit in the 2014 midterm elections, would be emboldened to argue that shortcomings with the law's implementation have jeopardized Americans' health.
As make-or-break January approaches, officials are also working to prevent gaps in coverage for millions of Americans whose individual policies were canceled this fall because they fell short of the law's requirements. In one of a series of last-minute tweaks, the administration in December said even if those individuals don't sign up for new plans, they won't face the penalty the law imposes on Americans who fail to get insurance by March 31.
A key indicator of whether state-run exchanges are keeping pace with the federal exchange will come next month, when the administration releases full December figures. Overall, the goal is to sign up 7 million Americans before the first-year open enrollment period closes at the end of March.
A few states offering their own updates have posted encouraging totals, including New York, where more than 200,000 have enrolled either through the state exchange or through Medicaid, a government program expanded under Obama's health law to cover more people. In California, a tally released Friday showed nearly 430,000 have enrolled through the exchange so far.
"The basic structure of that law is working despite all the problems —despite the website problems, despite the messaging problems," Obama told reporters before departing for Hawaii.
Another major unknown is whether the recent surge in enrollments skewed toward older Americans whose medical needs are expensive to cover, or whether the administration succeeded in recruiting younger and healthier people whose participation is critical to the law's success. Those details for December are expected to be released in mid-January.
Meanwhile, with the website now able to handle higher volumes without crashing or clogging up, the government plans in January to ramp up outreach to consumers to encourage more people to sign up, the administration said.
Reach Josh Lederman at http://twitter.com/joshledermanAP
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