The number of American middle and high schoolers using e-cigarettes declined dramatically in 2020 compared to last year, an official report showed Wednesday.

The drop came after a large outbreak of e-cigarette linked lung disease last year, and after the US government made legal changes to curb youth vaping.

About 3.6 million young people in the US were current (in the past 30 days) e-cigarette users in 2020, down from 5.4 million in 2019, according to the National Youth Tobacco Survey.

"Although the decline in e-cigarette use among our Nation's youth is a notable public health achievement, our work is far from over," said Robert Redfield, director of the Centers for Disease Control and Prevention (CDC).

"Youth e-cigarette use remains an epidemic, and CDC is committed to supporting efforts to protect youth from this preventable health risk."

The self-administered survey was taken between January 16 and March 16 by around 20,000 grade 6-12 school students, who are generally aged between 11 and 18.

The end date was before most regions in the US had gone into Covid-19 lockdowns so school closures were probably not a major driver of the reported decline.

Last year's outbreak of vaping-associated lung injury, which led to 2,700 hospitalizations and 60 deaths, could have been a deterrent.

Flavored e-cigarettes remain popular

The Centers for Disease Control and Prevention (CDC) eventually identified Vitamin E acetate, an additive in certain illicit THC-vaping products, as a primary culprit.

In 2020, approximately one in five high school students and one in 20 middle school students were current e-cigarette users.

Last year the equivalent figures were just over a quarter of high school students and one in 10 middle school students.

E-cigarettes entered the US market in 2007 and have been the most commonly used tobacco product among American youths since 2014.

To curb youth vaping, the Trump administration earlier this year barred flavors from smaller e-cigarettes that use pods, such as those made by market leader Juul.

Tank-based rechargeable vaping devices, primarily sold in vape shops, were left exempt.

US lawmakers also raised the federal minimum age for tobacco and e-cigarette sales from 18 to 21 in December 2019.

The 2020 survey showed that flavors such as fruit, mint or menthol remained favored by youth e-cigarette users.

Eighty-three percent of high school vapers reported using flavors and 74 percent of middle school vapers reported the same.

Pre-filled pod or cartridge-based e-cigarettes were the most commonly used device among youth vapers.

However, from 2019 to 2020, disposable e-cigarette use increased from two percent to 27 percent among high school users (a 1,000 percent increase).

Disposable e-cigarette use grew from three percent to 15 percent among middle school users, or a 400 percent rise.