Washington (CNN)About 16.4 million people have gained health insurance coverage since the Affordable Care Act became law nearly five years ago, according to government estimates released Monday.
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New Obamacare numbers: 16.4 million covered
The coverage gains have delivered the largest drop in the uninsured rate in four decades, bringing that rate down to 13.2% by the end of the first quarter of 2015, the Department of Health and Human Services announced Monday. That's down from about 20% before the health insurance marketplaces launched in late 2013.
Health and Human Services Secretary Sylvia Burwell said the numbers prove "the Affordable Care Act is working, and families, businesses and taxpayers are better off as a result."
Burwell credited the drop to key provisions of Obama's signature health reform law, from the expansion of Medicaid to new tax credits and a provision allowing young people under 26 to stay on their parents' health care plans.
About 2.3 million of the 16.4 million who have gained coverage under Obamacare are adults under 26 who were able to remain on their parents' plan.
Obamacare delivered the biggest gains among Latinos, for whom the uninsured rate fell by 12.3% since the first enrollment period in Oct. 2013. The uninsured rate among Latinos remains the highest, though, with about 29.5% of Latinos lacking health coverage.
The uninsured rate among African-Americans has been nearly halved -- dropping to 13.2% from 22.4% -- and 5% more white Americans are now insured.
The health insurance law has remained a lightning rod among Republicans and conservatives who continue to slam the law as a government overreach.
The Supreme Court is expected to rule on the latest challenge to Obamacare this summer -- about three years after the Supreme Court upheld the law as constitutional. The latest challenge specifically tackles subsidies under the law.
Republicans in Congress have vowed to fight for the law's repeal, but in the face of Democratic opposition to a full repeal and the threat of President Barack Obama's veto, it is all but certain the law will remain through Obama's presidency.