Asked Friday if the number of current sign-ups has led officials to raise their enrollment target, Slavitt said, that the information is "too new" and "too fresh" to make such an adjustment.
"We haven't begun to think about things like projections," he said.
Kevin Counihan, CEO of HealthCare.gov, said, "No one is running any victory laps. There's still work to do."
He noted that health officials are "targeting a tougher segment of the population to attract," a reference to the 10.5 million or so eligible uninsured people, many of whom are low income and have little familiarity with buying and using health insurance.
But, he added, 'We're encouraged by the results we've seen so far."
Counihan said he was also pleased by the fact that many returning customers were actively shopping for insurance instead of passively accepting re-enrollment, or opting out of coverage for next year.
"Since open enrollment began, the majority of our current marketplace consumers came back to shop and actively selected a plan for 2016, compared to last year, when we had about a third of consumers return and actively select a plan by the Dec. 15 deadline," he said.
Counihan on Friday noted that more than 8 out of 10 Obamacare exchange customers qualify for subsidies that help offset the cost of their coverage because they have low or moderate incomes.
About 7 out of 10 returning customers, officials have said, would be able to enroll in health plans that would cost them $75 or less after those subsidies are factored in.
People who don't have health coverage next year are subject to a potential Obamacare penalty, which is the higher of $695 per adult, or 2.5 percent of household income.
Correction: The 2.4 million new customers is one-third more than the amount of new customers seen at the same time last year. An earlier version misstated this fact.