About half the states have expanded Medicaid eligibility.  In states that did not, many poor adults are barred from Medicaid and from receiving federal subsidies to offset the cost of private Obamacare plans, which are available to people earning more than them.  That so-called coverage gap resulted from the Supreme Court decision that upheld Obamacare's legality, while leaving Medicaid expansion decisions up to individual states.  Although open enrollment in Obamacare private plans ended Monday, the total number of people insured via the exchanges will likely grow in coming months.  Read MoreActavis: See positive impact from Obamacare  An unknown number of people have been granted a grace period this month to finish the enrollment process they began on the exchanges before the deadline, but were unable to complete because of technical snarls. The deadline for such enrollments on HealthCare.gov, the federal exchange selling insurance in 36 states, is April 15, a date that has also been selected by several state-run exchanges with grace periods.  Others will be allowed to enroll in private plans if they have so-called qualifying life events, such as losing their employer's health coverage, getting married or divorced, or having a child. And enrollment in Medicaid or the CHIP program, a government plan that covers children, is open year-round.  Timothy Jost, a professor at Washington and Lee University School of Law and an expert in the health-care reform law, said he expects continued growth in the numbers of newly insured people this year, particularly in Medicaid expansion states.  Jost also predicted that the numbers of uninsured who signed up on the exchanges in March is "going to make a significant difference" in the overall uninsured rate.  "We're not going to get there," Jost said, referring to the CBO's estimate of 13 million newly insured people this year.  But, "we're going to get closer," he said.
At least 5.4 million people without health insurance have obtained coverage since September—and that number is likely climb in coming weeks.