WASHINGTON—The number of uninsured people in the U.S. remained at a historic low in early 2016, according to a federal survey that found 8.6% of respondents without health coverage at the time of the interview.

That translates to about 27.3 million people who lacked medical insurance when they were asked about it between January and March as part of the Centers for Disease Control and Prevention’s National Health Interview Survey. The previous survey, covering the whole of 2015, had put the figure at 9.1%, or about 1.3 million...