Maybe take a look at this:
http://www.e-cigarette-forum.com/fo...hen-quitting-tobacco-changing-ecigarette.html
There is no short answer to your question, and there is no straightforward, honest answer, unless it is phrased as a scientist would:
"Currently we have seen remarkably few credible adverse events that can reasonably be associated with vaping rather than the previous smoking history, or with smoking cessation - which has numerous well-documented minor morbidities associated with it.
Because of this, and the relatively large userbase already in place for this new technology (circa 25 million globally), and the significant timescale we already have experience of the products for (c. 9 years), and the fact we are already close to halfway to a 20 year mark that most clinicians would consider appropriate for evaluating the health impact of vaping, without any serious issues being revealed, then it is probably accurate to suggest that the health impact of vaping will eventually be shown as orders of magnitude less than for smoking. Indeed, it would be no surprise to learn that any serious health issues are not clinically significant. Equally, there will probably be multiple minor issues such as bronchitis in some individuals, for all sorts of reasons such as intolerance to specific brand ingredients or individual susceptibility to lung issues for genetic reasons - but the majority of these should prove reversible. It would be no surprise to learn of infrequent deaths of smokers or ex-smokers who vape, but it is difficult or impossible in practice to differentiate between various causes, such as the previous smoking history, which is highly likely to be the primary cause."
I tried to make this honest and accurate, in the style of a clinician with intimate knowledge of the issues. It's not a 10-word answer though.
The short version is: after about 9 years of vaping in the West, we have no reason to think there might be any serious problems, except possibly for those who go too far - as any honest person will admit.