It's a bit pointless trying to decide 'how addictive' ecigs are when many smokers or ex-smokers need nicotine and it's impossible to differentiate between needing a nic hit and needing a vape - they are the same thing. Now if you want to measure how 'addictive' ecigs are for never-smokers, then that is a better test. The answer is: it is impossible to create nicotine dependency in clinical trials without
tobacco, so ecigs can't be 'addictive'.
If you ran a clinical trial of ecigs for dependency potential, with the usual 30 or 40 subjects, and if they were all never-smokers, then you would get a result of zero. No one would be dependent on ecigs by the end of the trial. If you had 100,000 subjects then you'd get a few. So it's not impossible given enough people, but the resulting numbers will be invisible statistically.
It's proven impossible to create any nicotine dependency at all in clinical trials. That is to say, if you take a bunch of people who have never consumed
tobacco, and then give them nicotine daily for 6 months, none of them become dependent (none get cravings, or withdrawal symptoms, or take up smoking, etc.) You can't create nicotine dependence without
tobacco. The MAOIs and possibly the WTAs in tobacco cause the synergy that creates dependence on nicotine.
Ecigs are highly effective for nicotine reduction because vapers routinely reduce the amount they consume, over time. Ask any 2-year vaper how ecigs compare with tobacco cigs for addiction and you'll be told there's no comparison. If a smoker goes out of the house for an hour or two and forgets their cigs and lighter there's a panic; if a 2-year vaper forgets their ecig they just shrug their shoulders and wait till they get back home for a vape. If a vaper finds themselves in hospital for a couple of days without their vape gear it's not really a problem; but as a smoker they wouldn't be able to think of anything else while in there.