A day after a stunning court decision that threatens a crucial component of Obamacare, the federal government said Wednesday that 10.3 million adults have become newly insured by the close of open enrollment in the new type of health coverage.
The new enrollments, which came in both Obamacare plans and in Medicaid plans that have expanded eligibility, led to a 5.2 percent drop in the nation's adult uninsured rate after taking into account several factors, officials said.
The study, being published Tuesday evening in the New England Journal of Medicine, comes on the heels of recent reports that also showed decreases in the overall uninsured rate since the Obamacare insurance exchanges launched last fall.
Like a prior study, the NEJM study found that Latinos, blacks and younger adults saw the biggest drops in their uninsured rate.
The number of people who gained coverage during that time frame is of keen interest in the health policy world because of debates about whether Obamacare will lead to a net reduction in the uninsured, or whether most enrollees in exchange-sold plans are merely replacing old plans rendered illegal by Affordable Care Act minimum standards. Open enrollment in Obamacare insurance ended in mid-April, while Medicaid enrollment continues year-round.
"According to the authors' findings, the uninsured rate for adults ages 18 to 64 fell from 21 percent in September 2013 to 16.3 percent in April 2014," HHS said in a press release announcing the study.
Read MoreAppeals court split on Obamacare subsidies
"After taking into account economic factors and pre-existing trends, this corresponded to a 5.2 percentage-point change, or 10.3 million adults gaining coverage."
"We are committed to providing every Americans with access to quality, affordable health services, and this study affirms that the Affordable Care Act has set us on a path toward achieving that goal," said Health and Human Services Secretary Sylvia Burwell.
The study found that states that have expanded their Medicaid programs to include nearly all poor adults saw bigger drops in their uninsured rates among that group than states that didn't.
In the 24 states that did not expand Medicaid eligibility, "the change in the uninsured rate among low-income adult populations was not statistically significant," HHS said in a press release.
"This study also reaffirms that expanding Medicaid under the Affordable Care Act is important for coverage, as well as a good deal for states," Burwell said. "To date, 26 states plus D.C. have moved forward with Medicaid expansion. We're hopeful the remaining states will come on board and we look forward to working closely with them."
Read More
The 2012 decision by the US Supreme Court that upheld most of Obamacare also left it up to individual states on whether to open up their Medicaid programs to most poor adults.
The federal government is footing 100 percent of the costs of insuring the newly eligible under Medicaid in so-called expansion states for the first three years, and then has committed to funding 90 percent of the costs thereafter. But as a result of opposition to Obamacare generally, concerns about additional costs, and objections to funding health coverage for able-bodied adults, nearly half the US states have refused to endorse expansion.
The NEJM study also found that about 4.4 million more adults than previously reported having a personal doctor. The study further found that 5.3 million fewer people reported having difficulties paying for medical care.
The study comes a day after an unusual split decision by two federal appeals court on a crucial component of Obamacare.
On Tuesday, an appeals court panel sitting in Washington, D.C., said that taxpayer-funded subsidies that helped nearly 5 million people buy private Obamacare insurance through the federally run exchange HealthCare.gov are illegal because such financial assistance can only be given to enrollees in state-run exchange plans. That panel relied on explicit languate in the Affordable Care Act.
Hours after that decision, panel of judges in the Fourth Circuit federal appeals court in Virginia, while finding the ACA language ambiguous, said the subsidies are legal.
For now, the subsidies remain in effect, as the Obama administration prepares to ask the full D.C. federal appeals court to reverse the panel's ruling. If the ruling is not reversed, the differing opinions between the two appeals courts is expected to be resolved by the US Supreme Court.
The stakes in the dispute are very high for the Obama administration.
The subsidies were granted to nearly 90 percent of enrollees in the 36 states served by HealthCare.gov, and in many cases led them to paying less than $100 in premiums per month.
Read MoreCourts could cause big Obamacare $$$ hike
If the subsidies were eliminated in those states, many people would find the insurance unaffordable.
And it would also destroy, in those 36 states, the looming Obamacare rule that mid- and large-sized employers offer affordable health coverage to their workers or pay a fine — also would cripple the rule that most individuals in the states obtain coverage or pay a fine.
The administration has repeatedly noted that the subsidies remain in effect nationally, and has also said it is confident the courts will ultimately uphold their legality.