Teen use of electronic cigarettes fell sharply in 2021, the second-consecutive year of big declines, according to the government’s annual National Youth Tobacco Survey.

This year, 11.3% of high school students reported that they currently vape — down from 19.6% in 2020 and strikingly lower than the 27.5% reported in 2019, according to a report of the survey issued Thursday by the Centers for Disease Control and Prevention.

Even with the drop, the survey found that more than 2 million high school and middle school students were currently using e-cigarettes. And because the declines came during the pandemic, some public health experts questioned whether the data really signaled a change in youth vaping trends over the long term.

But some outside experts suggested that the big decrease in electronic cigarettes use is likely real and makes sense given that many U.S. students were forced to learn from home during the pandemic and young people often vape socially.

E-cigarettes came on the market in the United States in the early 2000s, promoted as devices designed to give smokers the nicotine fix they craved without the carcinogens that come from burning cigarettes. But they began to catch on with teenagers who had never smoked, and in 2018, the Food and Drug Administration warned of an epidemic of vaping among teenagers who were becoming addicted to nicotine through e-cigarettes.

In a statement, Mitch Zeller, director of the FDA’s Center for Tobacco Products, said the new data remained concerning, particularly the popularity of flavored e-cigarettes, which were banned by the Trump administration but remain on the market in certain forms through a regulatory loophole. According to the report, nearly 85% of youth e-cigarette users said they used flavored products. The most-common flavors were fruit flavors, but also included candy, mint and menthol — consistent with prior years.

“We are equally disturbed by the quarter of high school students who use e-cigarettes and say they vape every single day,” Zeller said, pointing to the data that shows 27% of regular users are daily users.

The American Heart Association also expressed concern.

“The results show that the crisis of e-cigarette use among youth remained very much alive even with kids spending large amounts of time at home during the pandemic,” the association said in a published statement. “With millions of children having returned to school this fall, immediate action is needed to prevent the sale of flavored e-cigarettes and other tobacco products, including menthol products.”

Another striking change was the decline in popularity of Juul, the once-dominant e-cigarette maker, whose sleek devices helped start the trend. Juul now sells only menthol and tobacco flavors, after the FDA banned flavored pods in early 2020.

The latest survey showed that Puff Bars, which sells a variety of flavors, is the most popular brand among youths, with 26% of regular high school e-cigarette users reporting Puff as “their usual brand.” Other popular brands include Vuse and Smok, while just 5.7% said their usual brand is Juul.

That change reflects a loophole in federal regulations that banned flavors for companies such as Juul that sell pods, but allowed flavors to be sold in disposable e-cigarettes. The loophole caused a surge in sales of disposables and in popularity among disposable brands, notably Puff Bars.

In 2021, disposables were most commonly used, by about 53% of youths who used e-cigarettes, followed by refillable or prefilled cartridges at 28.7%. A year ago, those figures were essentially flipped, with prefilled pods and cartridges leading and disposables taking a distant second.

The CDC and the FDA, which regulates e-cigarettes and tobacco products, emphasized that the year-to-year comparisons are complicated by changes to data collection: In 2021, because of the pandemic, youth responses were gathered entirely electronically, through online questionnaires, whereas the data had previously been conducted in classroom surveys.

These data have considerable implications for ongoing policy decisions currently in front of the FDA. The agency is deciding which companies can be allowed to remain on the market, following a review of whether the companies can show that they provide more public benefit — by helping smokers quit cigarettes — than harm, by creating new nicotine addicts.

Associated Press contributed.