The majority of the more than 2 million Americans who signed up for health insurance under ObamaCare through the end of December were already enrolled in employer-sponsored plans or had previously bought their own coverage, The Wall Street Journal reported Friday.

Early data from insurers, brokers and consultants suggest that the marketplaces are popular with consumers who were previously covered elsewhere, raising questions about a law intended to expand coverage to millions of healthy, uninsured Americans to help offset costs.

A survey by management consulting firm McKinsey & Co. found that only 11 percent of consumers who purchased new coverage under ObamaCare were previously uninsured. The survey was based on a sampling of 4,563 consumers between November and January, according to The Wall Street Journal.

HealthMarkets Inc., an insurance agency that signed up about 7,500 people in exchange plans, reported that 65 of its enrollees had prior coverage, the report said. Fifteen percent of enrollees had their individual plans canceled, and 40 percent switched over from previous individual plans.

"One of the intents of the law was to address the uninsured problem in our country," David M. Cordani, chief executive of insurer Cigna, told the newspaper. Some insurers said the early data on newly insured consumers is falling short of expectations.

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Insurers in Michigan expected 400,000 of the state's 1.2 million uninsured people to join private plans this year, according to an analysis provided Michigan-based Priority Health. As of the end of December, only 76,000 people had signed up, many of whom were previously covered, according to the report.

"I don't know we're growing the number of people with insurance here, so much as we're just adding complexity," Geoff Bartsh, vice president for policy at Minneapolis-based Medica Health Plans, told the Journal.

Federal health officials told the newspaper they don't yet know the number of people who have signed up for coverage through the exchanges who had insurance when they enrolled. Consumers have until the end of March 31 to purchase plans under ObamaCare.

"We are in the middle of a sustained six-month open-enrollment period, and we have seen a strong interest in the product overall across the range of demographics so far," said Aaron Albright, a spokesman for the Centers for Medicare and Medicaid Services. "We are ramping up outreach activities so that more Americans learn how they can now benefit from affordable health insurance."

Overall, adults ages 55-64 were the most heavily represented in the signups, accounting for 33 percent of the total. Nationwide, the premiums paid by people in that demographic don't fully cover their medical expenses. Some are in the waiting room for Medicare; that coverage starts at age 65.

Young adults from 18 to 34 are only 24 percent of total enrollment, the Obama administration said Monday in its first signup figures broken down for age, gender and other details. Enrolling young and healthy people is important because they generally pay more into the system than they take out, subsidizing older adults.

The Associated Press contributed to this report.

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