One quarter of new sign-ups are ages 18 to 34, far fewer than the 38 percent the administration had projected to keep premiums down but about what officials said they had expected at this point in the open enrollment period.
The one-month enrollment increase here was dramatic: 81,320 Pennsylvanians had selected coverage through the federal exchange by the end of December, a more than sevenfold jump from the month before. In New Jersey, 34,751 selected plans, up more than 10 times.
In both states, as nationally, more than three-quarters of them will have their premiums subsidized by the federal government. Nearly two-thirds of enrollees chose midlevel silver plans, which for certain incomes draw help with out-of-pocket costs in addition to the premium subsidies.
Policy analysts have expressed concern in recent days that too few young people might sign up, causing premiums to rise in what some termed a "death spiral."
Three researchers at the Kaiser Family Foundation published an analysis last month saying that if young adults made up just 21 percent of enrollees - far below expectations - individual market plans would exceed premium revenues by 2.4 percent.
The new enrollment numbers for the first three months released Monday are only slightly higher than that: Young adults account for 24 percent of sign-ups. Avalere Health, a consulting firm, said Monday that older and sicker individuals will enroll early in the open enrollment period, while younger, healthier individuals will sign up closer to the March 31 deadline.
"The insurance market will be stable with an enrollment mix like this," added Larry Levitt, senior vice president at Kaiser and a coauthor of last month's analysis, in an e-mail Monday. "But heightened outreach to young people, and even more importantly healthy people, will help to keep premiums down."
The enrollment breakdowns in Pennsylvania and New Jersey were close to national averages. Notably different between the two states was the number of people who applied for insurance through the federal exchange and were found to be eligible for Medicaid or the Children's Health Insurance Program (CHIP).
In Pennsylvania, which has not yet accepted Obamacare's expansion of Medicaid, the Marketplace found that 17,897 residents would be eligible; their files were said to be forwarded to the state.
In New Jersey, one of 25 states that has accepted the Medicaid expansion, 71,142 people were determined to be eligible for Medicaid or CHIP.
"New Jersey is leaning over backwards" to sign people up for insurance, said Raymond Castro, senior policy analyst at New Jersey Policy Perspective.
But do they have it?
Jeanne Patterson of Drexel Hill did when stomach pain drove her to go to the ER on New Year's Day.
Or so she thought.
In mid-December Patterson bought an Independence Blue Cross plan on the HealthCare.gov site. A few days later she got a letter from the insurer confirming her enrollment along with a temporary identification number.
But when she tried to use her insurance the day it kicked in, she learned the hospital considered her uninsured.
"They were very nice," Patterson said. "They said sign the form that you will self-pay and we will try to work it out."
Patterson, who also had to cancel an appointment with her primary care doctor, estimated that she spent eight hours over several days trying to get through to the insurer.
"I would call Independence Blue Cross in the morning, afternoon and night," she said. "I would put it on speaker and be on my computer or watch a movie. One time I got through and got somebody and they said, 'OK, I'll transfer you and stay on the line until you speak to someone.' But that didn't go anywhere."
It went right to the top after Patterson contacted CNNMoney.com. Brian Lobley, the insurer's senior vice president of marketing and consumer business, said Patterson's insurance could have easily been verified through NaviNet, an online portal the insurer gives to hospitals and doctors.
Lobley said one factor in the delays is that Independence is receiving on average 20,000 calls a day, about 28 percent higher than last January.
"A large majority of calls are the uninsured that are buying coverage, which is a good thing," he said. "However, they don't know how to use their coverage. Therefore we are dealing with unprecedented call volume. On New Year's Day our call volume was eight times" the holiday last year.
Independence has ramped up its customer service staff and is also directing customers to social media to relieve the telephone logjam.
Aetna spokeswoman Susan Millerick said that while the firm is fielding questions about identification cards and payments, it has not seen an increase in calls from people having trouble accessing their benefits.
Patterson has been assured by her primary care physician's office that insurance won't be a problem for her forthcoming appointment.
"It looks like it was straightened out. But you never know."
This article was produced in partnership with Kaiser Health News, an editorially independent program of the Henry J. Kaiser Family Foundation, a nonprofit, nonpartisan health-policy research and communication organization not affiliated with Kaiser Permanente.