Teenagers’ use of e-cigarettes fell sharply last year, while overall tobacco use declined to a new low, according to data that some anti-smoking advocates said could signal a turning point in the decades-long effort against youth smoking.

The Centers for Disease Control and Prevention’s annual report on youth and tobacco found that 11.3 percent of high school students used e-cigarettes in 2016, compared with 16 percent the year before. That’s the first drop since the CDC started keeping track of e-cigarettes in 2011.

In addition, just 8 percent of high-schoolers smoked cigarettes last year, while a little over 20 percent reported using “any tobacco product,” which includes cigars, hookahs, pipes, smokeless tobacco and small, leaf-wrapped cigarettes called bidis, as well as regular and e-cigarettes. Both those numbers are the lowest on record, the agency said.

“This is unimaginable, extraordinary progress,” said Matthew Myers, president of the nonprofit Campaign for Tobacco-Free Kids, noting that nearly 30 percent of young people smoked cigarettes in 2000. “This is a change of a cosmic nature that has the potential to dramatically impact lung cancer, heart disease, asthma and other problems.”

At the same time, he and other anti-tobacco advocates warned that the number of young people using tobacco products – 3.9 million high school and middle school students – was still much too high. They warn that progress could be derailed, especially if the Trump administration weakens the regulation of e-cigarettes and certain other tobacco products. It has already delayed enforcement of some tobacco regulations.

Robin Koval, president and chief executive of Truth Initiative, a nonprofit that focuses on tobacco use by young people, said the report suggests that the United States could be “well on our way to finishing smoking for good.” But she cautioned that the picture was very uneven among subgroups, with the high school smoking rate in West Virginia more than double the rate in California, for example.

She also said that the rapid decline in e-cigarettes among high schoolers suggests much of that use “has been experimental and that the current offering of products may be less appealing” than had once been feared. But she added that the rapid innovation in the e-cigarette industry “underscores the urgency for full implementation of FDA regulation” of the products.

The Food and Drug Administration asserted its authority to regulate e-cigarettes and some other products in 2016. But in early May, it delayed for three months the enforcement of some regulations that were to be imposed for the first time on e-cigarettes and cigars.

The delay came as the vaping and tobacco industries have launched a concerted effort to roll back the FDA regulations through both legislation and litigation. The e-cigarette industry, which includes small vaping businesses as well as the large tobacco companies, has said the rules are onerous and will drive them out of business. They say that e-cigarettes are safer than conventional cigarettes and should not be targeted. (Some aspects of the rules, including a ban on the sale of e-cigarettes and cigars to minors, went into effect last year.)

The three-month delay was announced a week before Scott Gottlieb was confirmed as FDA commissioner. In a statement Thursday about the new CDC data, Gottlieb said that while the latest numbers “are encouraging, it is critical that we work to ensure this downward trend continues over the long term across all tobacco products.” He said the agency has issued more than 4,000 warning letters to brick-and-mortar and online retailers for selling newly-regulated tobacco products, such as e-cigarettes and cigars, to minors.

Myers, of Tobacco-Free Kids, said that the report’s good news “is balanced by the fact that the very regulatory structure and programs that have helped bring it about are now being threatened.” Referring to Gottlieb, he added, “he comes in at a critical time. If he delays or weakens the rules over e-cigarettes he threatens the progress we are making with kids. If however, he vigorously implements them even while exploring whether e-cigarettes can help adults quit, he has the potential to turn the current trend into an irreversible movement.”

To determine how many young people are using tobacco products, the CDC asks them whether they have used it in the past 30 days.

Brian King, the senior author of the CDC report, said the decrease in e-cigarette use is likely a result of several factors, including efforts by the government and public health groups to educate young people about possible hazards of the products. While they don’t contain some of the harmful substances in conventional cigarettes, he said, the inhaled vapor usually contains nicotine, which is highly addictive and can harm the adolescent brain, as well as ultrafine particulates and heavy metals.

King also said that declines in tobacco use also are partly due to increases in state and local tobacco taxes, as well as the inclusion of e-cigarettes in antismoking ordinances barring smoking in restaurants, bars and other sites. The federal government and some nonprofits have also mounted campaigns warning about the dangers of smoking.

For example, the FDA’s “Real Cost” campaign, Gottlieb said in his statement, has helped prevent nearly 350,000 kids from smoking since its launch in 2014, while the Truth Initiative has run “truth,” a campaign featuring hard-hitting messages on the tobacco industry and its marketing tactics. CDC’s “Tips from Former Smokers,” aimed more at adults, also highlights the dangers of tobacco.