The proportion of U.S. adults without health insurance declined 5.2 percentage points since October 2013, with an estimated 10.3 million adults gaining coverage, according to a new study by researchers at the Department of Health and Human Services. Using survey data from the Gallup-Healthways Well-Being Index and HHS enrollment statistics for Medicaid and marketplace coverage, the authors estimate that the uninsured rate for adults under age 65 fell from 21% in September 2013 to 16.3% in April 2014, a 5.2 point change after adjusting for economic factors and pre-existing trends. The decline coincides with the initial open enrollment period for the Affordable Care Act’s health insurance marketplaces for uninsured adults and families. Coverage gains were concentrated among low-income adults in states expanding Medicaid under the ACA, and among individuals in the income range eligible for marketplace subsidies, the authors said. The study was published online by the New England Journal of Medicine.