Burwell underscored the importance of having HealthCare.gov, via desktop or mobile devices, make the bulk of enrollments, instead of having people fill out paper applications as an alternative.
"We want things to happen and occur online as much as possible," she said. "We would like to see more people online."
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Burwell expects improving access to the site via mobile can help grab young adults and Latinos, who use smartphones and mobile devices more than the nation as a whole.
The CBO projects total enrollment, which will include renewals in Obamacare plans and new customers, will be 13 million people by Feb. 15. But Burwell demurred when asked about her own target goal, saying "We're trying to build that number bottom up."
Burwell also punted when asked her goal for retaining a certain number of current Obamacare enrollments this season.
"We don't have a specific number on that," she said, adding that her department is working with insurers on "analytics" related to that question.
The number of re-enrollments will be closely watched because it will give an indication of how affordable people find their health plans to be, and how satisfied they are with the medical benefits, the service providers and customer service they get from their plans.
Any marked drop in the number of current customers will be seized on by Obamacare critics.
This year, the second of Obamacare enrollment, is the first year that people can renew their current plans. Burwell announced over the summer that most of the people currently enrolled through HealthCare.gov will be automatically re-enrolled in their plan, although they can choose another one if they prefer.
That re-enrollment program has several inherent risks. If people accept the re-enrollment without any thought or shopping for other plans, they may not only end up in a plan that is better suited to their needs, they also might end up getting less benefit from federal subsidies to help pay for their monthly premiums.
Burwell noted HealthCare.gov CEO Kevin Counihan said earlier this week that officials want to make automatic re-enrollment "as simple as possible."
But she also said HHS suggests "the importance of people ... going shopping" on that exchange for the best plan for their needs and pocketbook, and not just assuming that re-enrollment is their best option.
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Both HealthCare.gov and insurers will inform people of how their subsidies could be affected by an automatic re-enrollment, Burwell said. The vast majority of Obamacare enrollees, around 85 percent, receive some form of subsidy due to their household income level.
Burwell also said that a 25 percent increase in the number of insurers selling plans on Obamacare exchanges including HealthCare.gov this year is a sign of the industry's growing confidence in the ability of the plans to sustain themselves in terms of the balance between healthy and less-healthy enrollees.