NEW YORK (TIP): More than 6.3 million Americans were deemed eligible for government healthcare plans for the poor since the October 1 launch of President Barack Obama‘s healthcare law through December, federal officials reported on Wednesday.

The swelling rolls for Medicaid and the Children’s Health Insurance Program (CHIP) reflect both an expansion of Medicaid under Obama’s Affordable Care Act (ACA) and what healthcare policy analysts call an “out-of-the-woodwork effect,” in which people who heard about Obamacare sought to obtain health insurance and discovered that they had qualified for Medicaid even before the law expanded eligibility.

“We have people who for the first time will have some health security that they never had before,” Kathleen Sebelius, secretary of the Department of Health and Human Services, said of the Medicaid numbers at the winter meeting of the U.S. Conference of Mayors in Washington, D.C. It was not clear how much credit goes to the healthcare law, however.

“What many people don’t read far enough to learn is that this number also can include people in some states who are eligible under pre-expansion — the woodwork effect — and whose Medicaid enrollment was simply renewed,” said Matt Salo, executive director of the National Association of Medicaid Directors. The 6.3 million people determined eligible for Medicaid or CHIP last fall swamps the 2.2 million people who had purchased private health insurance on the state-based Obamacare marketplaces that launched on Oct. 1.

The ACA also raised the income threshold for Medicaid eligibility to 138 percent of the federal poverty level, or $15,856 for a single person. A Supreme Court decision in 2012 allowed each U.S. state to decide whether to accept the expansion. So far, 25 states have reached an agreement with the administration to do so. Prior to the ACA, just over 60 million Americans were covered by Medicaid. In December alone, 2.3 million individuals were determined eligible to enroll in Medicaid or CHIP, an increase of over 20 percent from November, according to the report from the Centers for Medicare & Medicaid Services (CMS), the lead Obamacare agency.

About 1.2 million of these were in the 25 states (and the District of Columbia) already expanding Medicaid, and just over 1 million were in the 25 states that have not. The CMS figures refer to the number of people that meet Medicaid eligibility rather than actual enrollment in the program due to the troubled HealthCare.gov website, which is run by the federal government to serve Obamacare sign-ups in 36 states.

For months, the website did not correctly transmit information that applicants are eligible for Medicaid to their state Medicaid program. The state offices do the actual enrollment, and have been scrambling to send out tens of thousands of letters to residents to actually enroll them, the Washington Post reported this month. At the same time, the national figures mirror what many of the Medicaid-expansion states have reported. In California, for instance, 625,000 individuals have gained coverage through private policies purchased on the state’s Obamacare exchange, Covered California, while 1.2 million enrolled in Medi-Cal, the state’s Medicaid program.

The websites through which people can shop for insurance under Obamacare are required to have what the Obama administration calls a “no wrong door” policy, meaning that even if people went to their state’s exchange expecting to buy private insurance, the site would determine if they were instead eligible for Medicaid or CHIP, which generally charge zero premiums. Several states have gone beyond that, seeking out Medicaid-eligible people by contacting those who receive food stamps or other benefits that indicate they have very low incomes