In week one (it was only three days long) of Open Enrollment for 2019, using the HealthCare.gov platform 371,676 individuals selected plans. Every week during Open Enrollment, the Centers for Medicare & Medicaid Services (CMS) will release enrollment snapshots for the HealthCare.gov platform, which is used by the Federally-facilitated Exchanges, the State Partnership Exchanges, and some State-based Exchanges.
Enrollment data can be obtained at https://www.cms.gov/newsroom/fact-sheets/weekly-enrollment-snapshot-week-1.