However, the Obama administration says it is optimistic it will see a surge of enrollees before the March 31 deadline for open enrollment this year, the Hill reported.
Department of Health and Human Service officials said an "action-forcing" event, such as the end of an open enrollment period, "often results in a spike in enrollment activity."
As of March 1, about 4.2 million people have enrolled in health plans through Affordable Care Act exchanges, the department said.
The number of people who actually bought coverage is likely to be significantly lower, the Hill said. Analysts estimate as many as 20 percent of enrollees haven't paid their first month's premium, meaning that about 840,000 of the 4.2 million enrolled don't actually have coverage.
Health and Human Services officials said the number of enrollees in the 18-to-34-year-old demographic was steady in February at 27 percent. The administration said it also expects the number of young enrollees to increase in March.