The pandemic dramatically decreased teen vaping, at least in the short term, said Bonnie Halpern-Felsher, a Stanford University developmental psychologist who studied young people’s vape use through the pandemic.

She published a study last month that found about two-thirds of participants (all ninth- and 10th-graders in California) either cut down or quit e-cigarette use during the pandemic. In another recent study, she and colleagues reported parallel results from a national survey of young people ages 13 to 24.

The decline is related to lockdown, she said, which interrupted teens’ lives just as much as everyone else’s—including the pathways they used to acquire vaping supplies. Now that school districts around the country are beginning to reopen, she’s concerned that many of those who cut down will pick the habit back up. 

But even before COVID-19, vape use had begun to decline, said Halpern-Felsher. In early 2019, some 20.8% of high school students and 4.9% of middle school students surveyed for the annual National Youth Tobacco Survey reported vaping in the past 30 days. The 2020 survey, which collected data between January and mid-March of that year, captured the state of youth smoking just before the pandemic. It showed a drop in those numbers: to 19.6% of high school students and 4.7% of middle schoolers. 

Despite the recent drops, “youth e-cigarette use remains high,” CDC chief epidemiologist of smoking and health Linda Neff told Fortune in an emailed statement.

Teen vaping became an issue in the 2010s, peaking three years after the 2015 market introduction of electronic-cigarette maker Juul’s discreet but potent pod-based vapes. In 2018, widespread use prompted the surgeon general to declare teen vaping an epidemic.

In the recent decreases, University of Arizona pharmacy science professor Ivo Abraham sees “some signals of growing awareness that this is not healthy.” As the COVID-19 pandemic wanes in the United States, it will be important to continue emphasizing the health risks of vaping to teens and other vulnerable populations, he and a colleague wrote in a commentary published in the scientific journal JAMA Open with the results of the 2020 National Youth Tobacco Study. 

Briana Choi, a University of Arizona Ph.D. candidate who was the lead author on that commentary, notes that COVID-19 itself also had an impact. “Because COVID was a lung-related disease, [teens] were also a little bit scared that vaping was going to make them sick,” she said. A new kind of lung disease connected to vaping, which rose to prominence in 2019 when several people died, likely also compounded that impression. 

As with cigarettes, public funds have been devoted to combating underage e-cigarette use, costs that some state governments have sought to recoup with lawsuits targeting Juul for seeking out the teen market. A 2019 white paper from Stanford researchers identified that the San Francisco startup’s advertising in its first six months on the market was “patently youth oriented” followed by years of more subtly courting teens. 

The new studies found that Juul still dominates among teen users, but disposable-vape maker Puff Bar is gaining. Unlike Juul, which voluntarily removed all flavored products except tobacco, mint, and menthol from its lineup in 2018, Puff Bar has remained on the market with fruit flavors, which public health experts say are appealing to teens. 

It’s too soon to tell what will happen with teen vaping, Abraham said. But the landscape is likely to change in the coming months, he noted, as the country continues to reopen and teens return to their old haunts.