The number of young Americans using e-cigarettes grew by 1.5 million in 2018, undermining years of progress in reducing youth smoking, health authorities said Monday.
Some 3.6 million middle and high school students were current users of vaping products, up from 2.1 million the year before, according to the report by the Centers for Disease Control and Prevention (CDC).
The CDC said the number of current cigarette smokers and consumers of other tobacco products in middle and high school remained roughly stable from 2017 to 2018.
A current user is defined as a person who has used a product in the past 30 days.
The CDC said 4.9 million middle and high school students were current users of some type of tobacco product in 2018, up from 3.6 million in 2017, with the growth attributed to e-cigarettes.
"This is the greatest single year-over-year increase that we've ever seen in terms of any tobacco products," said Brian King, deputy director for research translation at the CDC's Office on Smoking and Health.
"And of course going back, we've seen consistent decline in tobacco product use for two decades," King said.
CDC Director Robert Redfield said the "skyrocketing" growth of young people's e-cigarette use over the past year threatens to erase progress made in reducing youth tobacco use.
"It's putting a new generation at risk for nicotine addiction," Redfield said.
The CDC said e-cigarette use among high school students who use tobacco products increased from 11.7 percent to 20.8 percent from 2017 to 2018 and from 3.3 percent to 4.9 percent among middle school students.
Amid the rise in youth usage of e-cigarettes, US authorities have tightened regulations, with market leader Juul -- particularly its flavored products -- coming under scrutiny.
"We are extraordinarily concerned about the ongoing appeal that all flavored tobacco products have on kids," said Mitch Zeller, Director of the Center for Tobacco Products at the Food and Drug Administration, which regulates vaping and in November restricted the sale of certain flavors.
"All policy options are on the table," Zeller warned.
- Age verification -
Vaping began to take off among young Americans in the 2010s, and overtook cigarette smoking in 2014.
While the number of middle and high school cigarette smokers has been falling steadily since 2011, the number of vapers has increased dramatically, from 1.5 percent to the 20.8 percent last year.
The survey estimates 4.9 percent of college students vape.
The US categorizes e-cigarettes as tobacco products, a definition not shared by all countries.
In November, Juul announced it was suspending in-store sales of various flavored products and scrapping its social media presence.
Juul flavors such as mango, fruit and creme will now only be available on the company's website, where it said it was adding additional age-verification measures.
The FDA has proposed to allow flavored e-cigarette products to be sold in stores only, not online. The changes are open to a public comment period lasting until June before they can take effect.
Battery-powered e-cigarettes heat a nicotine liquid that users inhale, and have been gaining popularity in the United States and abroad.
E-cigarettes expose users to significantly lower levels of potentially toxic substances than traditional cigarettes, except for nicotine, the US National Academies of Sciences, Engineering and Medicine said last year.