The share of uninsured Americans dipped slightly last year, as more children and near elderly gained health coverage.

The share of uninsured people decreased to 15.4%, from 15.7% a year earlier, according to a Census Bureau report released Tuesday. Some 48 million people were uninsured in 2012, which was not statistically different from the prior year.

Last year, the number of uninsured Americans fell for the first time in four years.

Meanwhile, the share of people relying on the government for health insurance edged up slightly to 32.6%, from 32.2% a year ago. Those covered by Medicaid was not statistically different from a year earlier at 16.4%, while Medicare coverage rose to 15.7%, up from 15.2%.

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The Census report comes a few months before a major component of the Affordable Care Act kicks in. Starting in 2014, all Americans will be required to have insurance, whether through their employer or the individual market. Americans who don't have company-sponsored coverage can enroll in insurance plans on state-based exchanges beginning on Oct. 1. About 24 million people are expected to obtain insurance through the exchanges by 2023, according to the Congressional Budget Office.

But Obamacare, as the act is known, did not have a major impact on insurance coverage in 2012, Census officials and experts said. They don't expect to see any significant impact until 2015, when the 2014 figures are reported.

The report does show that companies were not dropping coverage in 2012, ahead of health reform. Some 54.9% of Americans had employment-based plans, not statistically changed from a year earlier, though down from nearly 63% over the past decade.

The two groups that did see coverage gains were children, who benefited from increased private insurance through their parents, and those age 55 to 64, who obtained plans through both employers and Medicaid, said Edwin Park, vice president for health policy at the Center on Budget and Policy Priorities, a left-leaning group.

The growth in overall Medicaid slowed, however, likely because the poverty rate also remained steady at 15%, said Brett O'Hara, chief of the health and disability statistics branch at Census. Meanwhile, the share of people on Medicare jumped as more Baby Boomers retired.

Whether they have insurance or not, people spent more on health care last year than in 2011. Those with coverage shelled out $2,707 in out-of-pocket expenses, up 4.8%. The uninsured spent $627, up 4.3%.