HARRISBURG - Toll-free phone lines were jammed, and low-income workers streamed into sign-up sites as enrollment opened Monday for expanded health insurance coverage under Medicaid.

An estimated 600,000 people - most working at low-wage jobs - are eligible for Medicaid through Healthy PA, the state's alternative to Medicaid expansion under the Affordable Care Act.

First-day enrollment numbers were unavailable, Kait Gillis, a spokeswoman for the Department of Human Services, said at the end of the day.

Even late in the day, callers to the state's toll-free line were told to call back later because of the high volume of calls. But Gillis said that "energy is high" and that there had been no reported online glitches.

"It's a historic day in Pennsylvania," she said.

The first day of enrollment comes more than 18 months after Gov. Corbett announced his proposal to seek federal approval for a Medicaid expansion alternative that would use federal dollars to pay for private health coverage.

The target population was those making too much for Medicaid and not enough to qualify for tax credits on the federal health insurance exchange.

For the more than two dozen states that expanded Medicaid, coverage began in January 2014.

Under new income guidelines, single adults, for instance, earning up to about $16,000 and a family of three making about $27,000 qualify. Coverage begins Jan. 1. There is no deadline to enroll.

Antoinette Kraus, director of the Pennsylvania Health Access Network, said that while she lamented that hundreds of thousands - many with chronic illnesses - had to wait a year to get coverage, she was happy the day had finally arrived.

"Hardworking Pennsylvanians have been waiting far too long for this day," said Kraus, who was part of a team helping to enroll individuals Monday at a library in Carlisle, west of Harrisburg.

She said people were "streaming in all day." Among them, she said, was a farmer who had to be turned away last year because his income was too high and whose health insurance premiums went up. He now qualifies for Medicaid. Several other individuals whose unemployment insurance had run out and could not afford private health insurance also enrolled.

Healthy PA, however, is likely not long for this world.

On Jan. 20, Gov.-elect Tom Wolf takes office, and he has vowed to scrap the Corbett plan - which critics say places limits on coverage for the most vulnerable - and shift immediately to full Medicaid expansion.

Wolf spokesman Jeffrey Sheridan said individuals would not lose coverage even though the transition will be cumbersome.

Individuals seeking insurance under Healthy PA can apply online at www.COMPASS.state.pa.us. They can learn more at www.healthypa.com, call 1-866-550-4355 or stop by their county assistance office.

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