(Bloomberg) -- Obamacare cut the share of people in the U.S. without health insurance by two percentage points this year, the U.S. Centers for Disease Control and Prevention said in a report today.

In the first three months of 2014, 18.4 percent of adults under age 65 lacked health insurance, down from 20.4 percent last year, according to the CDC survey. The fall in the uninsured rate was helped by 3.7 million people who bought private health insurance sold under the Patient Protection and Affordable Care Act, the CDC said.

The U.S. Census released a separate report today finding that about 42 million Americans lacked health insurance in all 2013. The Census’s data isn’t as current as the CDC’s, though it will serve as a baseline to measure Obamacare’s impact on health insurance coverage in future years.

While studies by outside researchers have recorded a drop in the U.S. uninsured rate this year, the CDC survey is the first official government report to register such a decline.

“Between 2013 and the first three months of 2014, there were significant decreases in the percentages of persons who were uninsured at the time of interview among persons of all ages,” according to the CDC report.

Both reports -- the Census department and the CDC’s -- fall short of capturing Obamacare’s full impact. The CDC’s 28,000- person survey didn’t count enrollment under the health law in late March and early April, when millions of coverage applications were accepted, while the Census report doesn’t take into account the enrollments at all.

Census Report

The Census report measured insurance coverage during 2013, the last year before the Affordable Care Act’s programs began. Unlike the CDC, it includes people over age 65 who get health coverage from the U.S.’s Medicare program. For the entire U.S. population, 13.4 percent of people were uninsured for all 2013.

The Census changed its methodology for its widely cited survey after 2012, when it said 48 million people lacked insurance. Because of that, the 2013 figure can’t be compared with prior years, the agency said.

“The survey improvements this year will better measure health insurance coverage for the prior calendar year, thus providing a strong 2013 baseline to measure future changes in health insurancecoverage caused by the Affordable Care Act,” the agency said in a statement.

Another study, published last month in the New England Journal of Medicine, estimated that about 10.3 million people gained insurance coverage under the health law this year.

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