New details about Obamacare insurance enrollment show that employer-based coverage is eroding, offsetting gains made in individual insurance enrollment, according to a report released today by The Heritage Foundation.

While individual coverage grew by 2.2 million Americans during Obamacare’s first open enrollment period, employer group coverage—health plans offered through the workplace—fell by 1.7 million, said the report, which is based on private coverage data from Mark Farrah Associates.

The drop in employer group coverage meant that net gains in new enrollment reached slightly more than 520,000 individuals during Obamacare’s first enrollment period, which ran from Oct. 1, 2013, to March 31.

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The Heritage figures did not include a month-long extension that the Obama administration and many states allowed for potential enrollees who faced problems signing up for coverage through the federal and state-run online insurance exchanges.

Meanwhile, enrollment in Medicaid and the Children’s Health Insurance Plan, two federal health programs for poorer individuals, jumped by nearly 5 million Americans during the same six-month period.

“It’s possible another 3 million to 4 million Americans gained individual coverage during that enrollment extension, but we won’t know until we see data for the second quarter of 2014,” said report co-author Edmund Haislmaier, a senior research fellow in health policy studies.

“But even if that happens and there’s no further decline in the employer coverage, you still have more than half of any increase in health coverage in 2014 coming from Obamacare’s expansion of Medicaid.”

The Obama administration said in May that 8 million Americans had signed up for plans on the Obamacare exchanges during the first enrollment period and extension.