At least two thirds of the 2.2M people who purchased health insurance from exchanges under Obamacare through December 28 already had coverage, preliminary surveys indicate.
In a McKinsey study, just 11% of people didn't have insurance previously. Affordability and technical problems were among the reasons why people didn't buy plans.
Around 48M Americans didn't have health insurance in 2012; Obamacare is expected to reduce that figure by 25M.
Meanwhile, the government is delaying yet another provision of the Affordable Care Act - one that prevents employers from offering better health benefits to senior management than to other staff. The reason is that tax officials haven't yet issued the regulations that companies need to abide by.
Just 30% of the people who have bought insurance under Obamacare are aged 34 or younger, while a third are 55 or older, a government report says.
That's a problem because the success of the Affordable Care Act hinges on signing up enough "young invincibles," who would need less care, in order to pay for the sick and elderly. The White House was banking on 40% of signups being aged 34 or less.
If the numbers don't balance out as needed, premiums could rise. Moreover, health insurers have until May to decide whether they will keep providing exchange plans in 2015.
Around 2.2M people bought coverage in the three months through December, 79% of whom received a discount due to federal subsidies.
National healthcare spending grew less than 4% for the fourth year in a row in 2012, rising 3.7% to $2.8T, a report by the Centers for Medicare & Medicaid Services shows.
As a proportion of the total economy, expenditure edged down to 17.2% from 17.3%.
The authors of the report said that the continued slow increase in spending was due to the lingering impact of the recession but that Obamacare has had a limited effect. However, the White House said the figures vindicated the President's signature policy.
The authors were also cautious about whether the trend will continue, or whether growth will return to the higher levels experienced prior to the recession.
The cost of hospital care rose 4.9% in 2012 and that for doctors' services and outpatient clinics 4.6%, although spending on prescription drugs increased just 0.4%, due to patent expiries.
Early reports from health providers and online medical booking service ZocDoc indicate that demand for care from those who bought insurance under Obamacare has been modest so far.
There have been fears that the technical problems of the government's HealthCare.gov Web site would cause a flood of patients who thought they had bought insurance to request care only to find that they weren't yet covered.
The actual pace of demand should give insurers more time to process the applications that they need to enter into their systems and issue membership cards.
More than 2.1M people have signed up for Obamacare-mandated health insurance, which has gone into effect today. That's an addition of 1.6M consumers in December, but somewhat below the 3.3M that was initially projected.
Administration officials also don't know how many people have paid, while insurers haven't received all the information they need about those who have bought plans. As a result, much confusion is expected when patients turn up for appointments, a situation the government is hoping to help alleviate with a toll-free call center.
Around 3.9M people are judged eligible for Medicaid and a related children's insurance program, although it's not known how many have signed up. Another 3M young Americans have coverage under their parents' plans.
Over 1.1M people had signed up for health insurance under Obamacare via the government's HealthCare.gov Web site by the Christmas Eve deadline after 975,000 bought coverage this month.
Combined with those who acquired plans in Washington DC and 14 states that operate their own exchanges, around 2M people have obtained insurance. The government had hoped that 3.3M people would have signed up by now.
The next major test will come on Wednesday onwards, when the coverage is due to start. There are widespread concerns that patients will turn up for appointments and treatments only to find that their insurance application didn't go through properly, or that their new plans don't cover them for the care they want or need. As a result patients have been rushing to carry out tests, procedures and elective visits before the end of the year.
Federal and state governments are continuing to let people sign up for health coverage that takes effect on January 1 even though the latest national deadline passed on Tuesday.
Those who were unable to buy plans because of the problems affecting Obamacare's HealthCare.gov can contact a call center to see if they can still purchase plans, while Massachusetts, Minnesota and Rhode Island are allowing residents to sign up as late as New Year's Eve.
The continued shifting of the deadlines comes amid a late surge in attempts to buy coverage, with 2M people visiting HealthCare.gov on Monday.
However, it's not going down well with health insurers, who believe they won't have enough time to process all these late applications.
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