In 2013, the year that full provisions of the Affordable Care Act began to go into effect, about 29 percent of West Virginia adults did not have health insurance.
Last year, about 9 percent of West Virginia adults did not have health insurance.
The 20 percentage point decline in the uninsured rate (for adults ages 18 to 64) in West Virginia is the largest of any state in the nation, according to new data released Tuesday from the federal Centers for Disease Control and Prevention.
Virtually every state saw significant declines in its uninsured rate, according to the CDC's National Health Interview Survey, an annual study based on more than 100,000 interviews nationwide. West Virginia's decline in the uninsured rate, though, is more than four points greater than the next-largest decline (Kentucky saw its uninsured rate fall by almost 16 percentage points) and more than double the national decline of 7.6 percentage points.
Nationwide, 7.4 million more people had health insurance in 2015 than in 2014, and the rate of uninsured - 9.1 percent for all people, 12.8 percent for adults - was the lowest the annual survey has ever found.
In West Virginia, those numbers also are at record lows - a 6.1 percent uninsured rate overall, and 8.9 percent for adults.
"Today's report is further proof that our country has made undeniable and historic strides, thanks to the Affordable Care Act," said Sylvia Burwell, secretary of the Department of Health and Human Services, and a Hinton native, in a prepared statement.
About 59 percent of West Virginia adults (ages 18 to 64) get health insurance through a private insurance provider, while about 35 percent get it through a public health plan - mostly Medicaid, but also military health insurance and Medicare, for those with disabilities.
West Virginia has the highest rate of adults on public health insurance of any state in the nation.
Other low-income states - Mississippi, Alabama and Louisiana, for instance - have not expanded Medicaid under the ACA and, thus, have much higher uninsured rates than West Virginia.
As of Monday, more than 175,000 West Virginians - nearly 10 percent of the population - were enrolled in the ACA's Medicaid expansion, according to the state Department of Health and Human Resources.
West Virginia's plunging uninsured rate is not solely because of the Medicaid expansion. It is about half attributable to increases in publicly provided health insurance and half attributable to increases in private plan enrollment.
Enrollment in public plans increased by 10 percentage points from 2013 to 2015, from about 25 percent of West Virginia's adult population to 35 percent.
Enrollment in private plans increased by the same 10 percentage points, from 49 percent of the population to 59 percent.
Reach David Gutman at david.gutman@wvgazettemail.com, 304-348-5119 or follow @davidlgutman on Twitter.