About 504,000 people selected plans during the week that started Nov. 19.
The Centers for Medicare and Medicaid Services (CMS), that runs HealthCare.gov, is publishing weekly activity reports this year and published biweekly reports last year.
About 1.3 million people signed up during the third and fourth weeks of the open enrollment period for 2018, up just 15% from the total for the third and fourth weeks of the open enrollment period for 2017 coverage.
But plan selection activity was about 40% higher during the first two weeks of the 2018 open enrollment period than it was during the first weeks of the 2017 open enrollment period.
CMS, a division of the U.S. Department of Health and Human Services (HHS), set the 2018 open enrollment period to run from Nov. 1 through Dec. 15 in the HealthCare.gov states.