Since e-cigs went on sale in 1997 in the US, they have reduced by a fifth smoking-related deaths in those born after their introduction.
Tobacco control experts argued while the numbers of teenagers now vaping has increased, the numbers actually smoking deadly tobacco has fallen.
Without the new devices, more teenagers and young adults would have smoked instead.
The team on international experts argued the health benefits of vaping outweighed any negative effects of teenagers taking up either e-cigs or real cigarettes.
Scientists had claimed e-cigs lead teenagers who vape to take up smoking.
But Professor of oncology Dr David Levy at Georgetown University Medical Centre said “recent claims by some scientists that e-cigarettes are likely to act as a gateway to the use of tobacco products are overstated.”
Computer modelling found e-cigs provide public health benefits based on “conservative estimates” of the likely uptake of vaping and smoking by adolescents and young adults.
Prof Levy said: “Our study indicates that, considering a broad range of reasonable scenarios, e-cigarettes are likely to reduce cigarette smoking and not lead to offsetting increases in harm from the use of e-cigarettes and more deadly cigarettes.
“When we consider the plausible positive and negative aspects of e-cigarette use, we find that vaping is likely to have a net positive public health impact.”
The model developed by US, Canadian and Australian scientists projected a reduction of 21 per cent in smoking-attributable deaths and 20 per cent in life years lost as a result of use of e-cigarettes in people born in 1997 or after, compared to what would have happened if e-cigarettes were not an option.
Prof Levy added: “Our model is consistent with recent evidence that, while e-cigarette use has markedly increased, cigarette smoking among youth and young adults has fallen dramatically.”
He backed the raising of the minimum age to buy e-cigs to 18 “because we still want to discourage use of all nicotine and cigarette products.”
He also said experts need to monitor how the market develops and how teenagers respond but warned against regulating e-cigarettes in the same manner as cigarettes.
He said this will pose a burden to smaller companies who will not have the resources necessary to gain marketing approval for their products against Big Tobacco.
He added: “Overregulation of e-cigarettes might actually stifle the development and marketing of safer products that could more effectively displace cigarettes.”
The study was published in Nicotine & Tobacco Research.