A man vapes at home in La Paz, Bolivia, on Saturday. (David Mercado/Reuters)

SMOKING IS an unmitigated public-health horror. But is vaping? Just when the case against e-cigarettes seemed to be growing stronger by the day, a new study presents a more complicated public-health picture: They seem to be bad for some but good for others.

The study, published last week in the New England Journal of Medicine, followed 886 British smokers seeking government help to quit. Along with a month of counseling, half were given traditional nicotine-replacement products, such as gum or patches, while the other half got e-cigarettes. After a year, researchers checked the carbon monoxide levels in their subjects’ breath, a test for cigarette smoking. Nearly a fifth of those who were given e-cigarettes still abstained from smoking, roughly double the proportion in the gum and patch group. The natural inference is that vaping, which mimics the experience of smoking more closely than other nicotine-replacement products, is a useful tool now for some smokers who want to quit.

So should public-health authorities be promoting e-cigarettes? If only it were so simple. The researchers also found that, among those who quit smoking, the e-cigarette group mostly continued to vape after a year, whereas the patch and gum group stopped using nicotine-replacement products entirely. E-cigarettes are surely much safer than traditional cigarettes, but their long-term effect is still unknown. There is reason for concern about the effects of chronic exposure to the chemicals in the nicotine-laced liquids that e-cigarettes vaporize for inhalation. A New England Journal of Medicine editorial noted that drug-based cessation therapy has a similar success rate to that just measured for e-cigarettes, suggesting that there are preferable alternatives to shunting smokers onto another nicotine inhalation device.

Moreover, making e-cigarettes easily available to smokers poses a risk to non-smoking teenagers, among whom e-cigarette use is skyrocketing. University of Michigan researchers found in December that vaping among high school seniors nearly doubled between 2017 and 2018. A fifth reported having vaped nicotine in the previous month. Nicotine is an exceptionally addictive drug that affects adolescent brain development, and public-health officials rightly worry that a generation of teenagers hooked on vaped nicotine will move on to more dangerous drug use.

In other words, the evidence commends neither the prohibition of e-cigarettes nor a welcoming embrace. Rather, the devices should be targeted at a defined subset of people: current smokers for whom patch, gum and drug therapy has not worked. The Food and Drug Administration should continue cracking down on the sale of vaping products to minors, restricting advertising and limiting the availability of flavorings that might appeal to children. Meanwhile, public-health authorities should support getting e-cigarettes into the hands of those who really need them.