NEW YORK (AP) — Teen vaping, which has been skyrocketing, fell dramatically last year in the United States.

A new government survey suggests the number of high school and middle school students using electronic cigarettes fell to 2.2 million last year, from 3 million the year before.

Health officials have worried about the booming popularity of vaping products among kids, and the potential impact the trend may have on adult smoking rates in the future.

The Centers for Disease Control and Prevention released the study Thursday. It’s the first decline CDC has reported in teen vaping since the agency began tracking in 2011. The results echo a University of Michigan survey that also detected a teen vaping decline in 2016.

Experts say it’s too soon to know if the numbers will continue to drop.