Obamacare private insurance plans had signed up almost 8.02 million people by April 19, the effective end of open enrollment in the new health coverage, officials said Thursday.
Nearly half — 47 percent — of total enrollment for the six-month sign-up period for Obamacare plans came in just the last seven weeks, officials said.
While there was significant variation in the enrollment success, or lack thereof, among individual states, the insurance risk pools created by Obamacare exchanges "in every state" are large enough and diverse enough to keep premium prices stable in 2015, predicted Mike Hash, director of health reform efforts at the Health and Human Services Department.
HHS also disclosed that an additional 4.8 million people were enrolled in government-provided Medicaid as of March 31, compared to Medicaid's total enrollment in October.
Health exchanges under the Affordable Care Act launched in October and began assessing whether individuals were eligible for private Obamacare plans or for Medicaid, which covers people with lower incomes. Many of the newly Medicaid-eligible people enrolled in that program via government-run exchanges. There is year-round enrollment in Medicaid, and about half of the states have loosened their eligibility rules to allow more poor adults to sign up.
The enrollment tally in the private exchange plans was not surprising, as President Barack Obama had already said two weeks ago that Obamacare sign-ups in such plans had topped 8 million.
That was 1 million more than what had been predicted last summer by the Congressional Budget Office. But nonetheless, it came as a surprise because of the botched launch of the federal HealthCare.gov exchange last fall, when serious technical glitches effectively crippled enrollment efforts for two whole months.
The final tally was bolstered by a dramatic wave of enrollments in the last six weeks of open enrollment, including a noticeable surge of younger adults whose participation in the exchanges had been lagging behind insurers' hopes. In three states whose Republican governors are hostile to Obamacare — Texas, Georgia and Florida — enrollment grew by 123 percent or more since March 1, officials said.
HHS Secretary Kathleen Sebelius, who announced her upcoming resignation last month, said the national enrollment tally exceeded expectations, and "demonstrated brisk demand for quality, affordable coverage."
But even with the 8,019,763 people who signed up since October for private insurance, tens of millions of people remain without health coverage in the US, despite Obamacare's mandate that nearly all Americans have such coverage as of this past March or face a tax penalty next year of up to 1 percent of their income. About 5.5 million people who filled out applications on the Obamacare exchanges didn't end up enrolling, according to data released Thursday.
However, the CBO recently estimated that an additional 5 million people have purchased individual plans outside of the Obamacare exchanges.
State health systems still getting a failing grade
Although open enrollment in Obamacare plans officially ended March 31, the effective close of enrollment for most of the country was April 19, as a result of waivers for people who ran into technical problems on the exchanges and other extensions. But additional sign-ups will still come from the state-run exchanges of Oregon, Nevada and Maryland, all of whom have some form of sign-up extension for at least one month.
Officials said that as of April 19, a total of 5.4 million people had enrolled in the 36 states served by HealthCare.gov, and another 2.6 million had signed-up using one of the 15 exchanges run by individual states and the District of Columbia.
Officials said that about 2.2 million of the reported private plan enrollments nationally—28 percent of the total—came from adults ages 18 to 34. That group is greatly desired by private insurers, who need premiums from that relatively healthy population to offset benefits paid to sicker, and often older, enrollees.
One in four enrollees was between the age of 55 and 64.
HHS said about 3.8 million people enrolled after March 2, and almost 1.2 million of them were young adults. Total enrollment after March 2 was nearly 90 percent more than the number of people who enrolled in the month of February.
Officials also said that 85 percent of the people who selected an insurance plan qualified for government subsidies to offset the cost of coverage because their incomes were either low or moderate.
And 54 percent of all enrollees were women.
But how many paid?
The federal government did not release data on what percentage of enrollees have paid their first month's premium, which is required for coverage to take effect. However, a number of state-run exchange, and individual insurers have been reporting the rate of paid sign-ups, generally saying they are in the range of 80 to 90 percent.
Julie Bataille, a spokeswoman for Sebelius, said that HHS wanted to make sure its data was accurate before releasing information about how many people made their first month premium payments.
"We're committed to providing it," Bataille said. But, she added, "I don't anticipate having it until later this year."
Likewise, HHS did not release information about enrollment tallies for each of the individual insurance plans sold on the Obamacare exchanges. A number of state-run exchanges have been routinely releasing such data.
When asked when HHS would disclose individual insurer tallies, Bataille said, "That's something that we'll have to look into and get back to you. I'm not aware of plans at this particular moment."
HHS did break out enrollment tallies for what types of insurance plans people picked. A total of 65 percent of Obamacare enrollees opted for so-called "silver plans," moderately priced policies. Another 20 percent chose bronze plans, which were the least expensive option for people who could use subsidies to offset the costs of their coverage.
The hotly debated question of how many Obamacare enrollees were people who needed to replace policies that were no longer compliant with Affordable Care Act standards was not answered in the enrollment report issued Thursday.
Officials said that 87 percent of people who applied for subsidies via the federal exchange HealthCare.gov — which sells policies in 36 states — reported lacking insurance at that time, in response to a question that was asked on that Web site. But officials told reporters that because of independent surveys which have shown that a majority of Obamacare enrollees had previously been insured, along with other factors, made the 87 percent uninsured statistic unreliable.
The release of the enrollment data came less than 24 hours after Republicans in the House said a recent survey they conducted of insurers found that only 67 percent of Obamacare enrollees who signed up on the federal HealthCare.gov exchange had paid their first month's premium as of April 15.
Insurers were not polled about their paid rate on plans sold on the 15 state- and DC-run exchanges.
The House Energy and Commerce Committee said the 67 percent figure cast serious doubt on the validity of the administration's claims on April 17 that a total of 8 million people had enrolled. The paid rate has become a major talking point for Obamacare opponents, who have blasted the administration for not revealing it while at the same time issuing raw sign-up data.
"In a sad reversal away from its vows of transparency, the Obama administration, from inside the Oval Office on down, has done to extraordinary lengths to keep basic details of the health law from the public," said committee chairman Rep. Fred Upton, R-Mich. "Tired of receiving incomplete pictures of enrollment in the health-care law, we went right to the source and found that the administration's recent declarations of success may be unfounded."
But his committee's claims were immediately attacked by the Obama administration, and other supporters of the ACA, who accused the Republicans of releasing data that was incomplete and premature.
Read More55% interest for a medical loan?! NY says no way
"These claims are based on only about half of the approximately 300 issuers in the federally facilitated marketplace [HealthCare.gov] and they do not match up with public comments from insurance companies themselves, most of which indicate that 80 to 90 percent of enrollees have paid their premium," said Erin Shields Britt, an HHS spokeswoman.
"Additionally, given the significant surge in enrollments at the end of March, it stands to reason that not all enrollees would have paid by the date of this so-called report since many people's bills were not even due yet."
'Jumbled mess'
Charles Gaba, a website developer whose Obamacare enrollment tracking blog site ACASignups.net has become a prime source for media covering enrollments after a series of accurate predictions, wrote in a post that the committee's report was "embarrassingly flawed."
"It's a jumbled mess," Gaba told CNBC.com. "It's misleading at best, and deliberately misleading at worst."
In his post, Gaba wrote, "Their 67 percent figure assumed that all enrollees as of 4/15 were supposed to be due by 4/15 (in fact only about 63 percent of the total enrollments were due by 4/15; the rest weren't due until yesterday, or even later depending on the insurance company."
"They curiously failed to include two states—Idaho and New Mexico—in their own state-by-state breakdown, even though both of those states were part of the Federal Marketplace," he continued.
Gaba also noted that in his home state of Michigan, insurers supposedly had told Congress that just 55 percent of total sign-ups on HealthCare.gov plans sold in the state had been followed by a first month's premium payment.
But, Gaba said, Blue Cross Blue Shield of Michigan, the state's largest insurer, has publicly said "that a whopping 95 percent of their enrollees are paid up."
Read MoreCoughing up big bucks for missing patient health data
"So, in order for the GOP's '55 percent in Michigan' to be accurate, they're basically saying that 95 percent of Blue Cross's customers paid . . . but NOT A SINGLE CUSTOMER has paid for any of the other 8 companies (HAP, Total Health Care, Alliance, Humana, McLaren, Priority Health and so on," Gaba wrote. "Somehow I find that extremely difficult to believe."
In apparent reaction to such critiques, Upton on Thursday posted a message on Twitter saying, "Despite prior denials, if @HHSGov does have detailed data on #WhosPaid, then let's see it. #Transparency now is better late than never."
—By CNBC's Dan Mangan.