That said, HealthCare.gov has seen a another big drop from its first week this season, when 1.032 million applied for determinations on whether they are eligible to buy insurance on the exchange. In the second week, just 520,427 people filed these applications, according to CMS.
There was also a sharp drop in the number of calls to HealthCare.gov's phone assistance center, from 1.7 million calls in enrollment's first week to just 484,867 calls in its second.
And the total number of users window-shopping for plans on HealthCare..gov dropped from 1.58 million in the first week, to just 716,192 in the second.
Health and Human Services Secretary Sylvia Burwell said, "The first deadline is just a couple of weeks away on Dec. 15. We're encouraging everyone who is already covered through the marketplace to come back and shop because there could be savings."
"We expect even more consumers to shop and save during the next two weeks," she said.
Burwell's newly instituted practice of issuing weekly updates during open enrollment contrasts with that of her predecessor at HHS, Kathleen Sebelius, who only authorized monthly enrollment updates despite requests by the media, Congress and analysts for more frequent data releases.
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The data release came on the same day that the Urban Institute published a report showing a sharp drop in the rate of people who lacked health insurance from September 2013, right before the Obamacare health insurance exchanges opened for business.
The Urban Institute said that between Sept. 2013 and Sept. 2014, the number of non-elderly adults without insurance fell by about 10.6 million people. And the rate of uninsurance among that same population dropped from 17.7 percent to 12.4 percent—a 30.1-percent plunge.
"Most of the gain in coverage was among the low- and middle-income adults targeted by the [Affordable Care Act's] Medicaid and marketplace provisions," the report noted.
The ACA, which is also known as Obamacare, allowed states to expanded eligibility for Medicaid programs to included nearly all poor adults. More than half of the states have expanded eligibility for that joint federal-state health coverage program for the poor.
Obamacare also gives people earning between one and four times the federal poverty level subsidies or tax credits to help them pay insurance premiums if they buy individual insurance coverage through HealthCare.gov or a state-run health exchange.
Burwell has said she expects there to be 9.1 million people enrolled in exchange-sold Obamacare plans by the end of 2015. Right before the start of this open-enrollment season there were about 6.7 million people enrolled in such plans.
Open enrollment runs through Feb. 15.
Under the ACA, most American adults must have some form of health-care coverage or pay a fine, which is equal to up to 2 percent of their taxable income in 2015.