If an average high school class contains 30 students, at least seven of them were tobacco users in 2015, according to a report released this week by the Centers for Disease Control and Prevention. Visit a middle school classroom of the same size, and about three of them regularly smoked, vaped or dipped.

That shakes out to around 4.7 million children and teenagers who use tobacco. Even more problematic, the report said, “Tobacco use and addiction mostly begin during youth and young adulthood.”

“If current smoking rates continue, 5.6 million Americans aged 18 who are alive today are projected to die prematurely from smoking-related disease,” the report said.

In 2015, with all the overwhelming scientific evidence of the inherent health risks, those numbers might seem strange — until one considers e-cigarettes.

Use of conventional cigarettes is actually down, but a drastic increase in e-cigarette usage among middle school and high school students from 2011 to 2015 — from 1.5 percent to 16 percent for high school students and from 0.6 percent to 5.3 percent for middle school students — has evened out the numbers. In other words, kids are using a different type of tobacco, but the number of tobacco users in general has not fallen.

Three million high school and middle school students used e-cigarettes last year, according to information released by the CDC Thursday. The rise isn’t new.

“Current e-cigarette use among middle and high school students tripled from 2013 to 2014,” the CDC wrote in a press release last April, when the number of users jumped drastically from 660,000 to 2 million for high school students and from 120,000 to 450,000 middle school students.

E-cigarettes, designed to vaporize nicotine and imbue the smoke with various flavors, generate an estimated $3.5 billion in annual sales.