About one in seven high school students (14.1%) reported earlier this year using e-cigarettes during the previous 30 days, according to a survey by the Food and Drug Administration and Centers for Disease Control and Prevention.

The poll, which was released Thursday, also found 3.3% of middle school students said they used e-cigarettes in the month before. In all, it adds up to an estimated 2.5 million U.S. youths vaping. 

Twenty-eight percent of adolescents who use e-cigarettes said they vape daily, the survey found. Forty-two percent reported using the products 20 or more days in the previous month.

The survey found that 85% of middle and high school students who vape use flavored e-cigarettes. Fruit flavors were the popular, at 69%, followed by candy, dessert or other sweets flavors (38%), mint (29%) and menthol (27%).

Puff Bar (14.5%) and Vuse (12.5%) were the most popular brands among adolescents. More than half  (55.3%) of middle and high school students who vape said they use disposable e-cigarette devices. A quarter (25.2%) said they prefer prefilled or refillable pods or cartridges, and 6.7% said they use tanks or mod systems.

The findings are based on data from this year’s self-administered National Youth Tobacco Survey, which was given to students from grades 6 to 12 from Jan. 18 to May 31.

“This study shows that our nation’s youth continue to be enticed and hooked by an expanding variety of e-cigarette brands delivering flavored nicotine,” said Deirdre Lawrence Kittner, director of the CDC’s Office on Smoking and Health. “Our work is far from over. It’s critical that we work together to prevent youth from starting to use any tobacco product — including e-cigarettes — and help all youth who do use them, to quit.”

The CDC said it’s difficult to compare this year’s findings to previous years because the COVID-19 pandemic affected the way the survey was administered and how data were collected in recent years.

“[D]ifferences between estimates might be due to changes in methodology, actual behavior, or both,” a CDC news release said.

The use of tobacco products by youths in any form is unsafe because the products contain nicotine, which is highly addictive and can harm brain development, the CDC says. Nicotine use during adolescence might also increase the risk for future drug addiction, the agency says.

Since 2014, e-cigarettes have been the most popular tobacco product among American youths, according to the 2021 National Youth Tobacco Survey.

“Adolescent e-cigarette use in the United States remains at concerning levels, and poses a serious public health risk to our nation’s youth,” said Brian King, director of the FDA’s Center for Tobacco Products. “Together with the CDC, protecting our nation’s youth from the dangers of tobacco products—including e-cigarettes—remains among the FDA’s highest priorities, and we are committed to combatting this issue with the breadth of our regulatory authorities.”