MIAMI, FL - MARCH 07: US President Barack Obama speaks during an event at Coral Reef Senior High on March 7, 2014 in Miami, Florida. Obama announced a program that will allow students an easier way to complete the Free Application for Federal Student Aid. (Photo by Joe Raedle/Getty Images)

More than 4.2 million people enrolled into private plans via Obamacare's health insurance exchange marketplaces through March 1, the Department of Health and Human Services announced in a report Tuesday.

The first open enrollment period on the exchanges, which are intended for individuals and families who don't get health benefits at work and aren't covered by government health care programs, ends March 31 for private coverage that will be in effect this year. At the current pace, sign-ups are below the original target of 5.6 million by the end of February, based on the Congressional Budget Office projection of 7 million by the end of March. Last month, the budget office downgraded those projections to 6 million total for the full six-month enrollment period, so a big surge would be needed in the final weeks to meet that benchmark.

One-quarter of the enrollments up to March 1 were for individuals between the ages of 18 and 34. This demographic is considered critical to the long-term viability of the state-based health insurance exchanges because they are presumed to be healthier and thus less likely to incur costly medical bills than the older people in the market. The White House originally aimed for about 40 percent of the enrollees to be younger than 35 years old.

The Department of Health and Human Services report doesn't include critical information about Obamacare sign-ups to date, including how many of the new customers have finalized their enrollments by paying premiums to their health insurance providers. The White House disclosed last month that total enrollments had surpassed 4 million. Vice President Joe Biden said last month that private insurance sign-ups on the exchanges would likely end up at around 5 million.

Uncertainty also remains about how many people have signed up for Medicaid or the Children's Health Insurance Program since open enrollment commenced Oct. 1. According to Tuesday's HHS report, 4.4 million people have signed up for Medicaid and the Children's Health Insurance Program since the beginning of the enrollment period. That number doesn't include anyone who enrolled in the programs directly with state agencies, however.