Two things are very different about vapor. One, the particulate size of the vapor is much larger than smoke, which means it doesn't get as far down into the lungs. It's the little bitty tiny pockets at the very end that are the most fragile. Vapor can't get that far, whereas smoke can. I can't remember where I saw this, but it may or may not have been from a major journal.
And even if it could, the cell toxicity (or how many cells are celled when in contact with the product of vaping or smoking) of pure PG/VG is 0. Flavored PG/VG is not 0, but it's close enough for jazz. If you soak the cells in the fluid, some of them might die, maybe, at very high concentrations of flavoring. Even nicotine bearing juice is only toxic at concentrations of 50% or higher AND it is far less than cigarette smoke, which is extremely toxic. It causes cell death at concentrations greater than 6.25%. This was from a juried journal article in I want to say New England Journal of Medicine. But it was a major, major journal.
Things in this field have changed, radically. If you look at the juried journals, like NEJM, they were all, "Uh, we don't know. It could be ... Maybe ..." Today, from articles published in late 2013 and 2014, it seems they've figured out it's definitely better than cigarette smoke and 0 nic is like taking a bubble bath. The studies for these articles were probably done a year or two ago (that's the turnaround for most major journals) and it usually takes at least a few years for the journals to hit the public.
I do have access to pretty much all the major journals, but anyone can get their hands on the abstracts through Google Scholar. Now this is not light reading but you can go to a medical research library or library for a major university and ask the librarian for help. If it's a medical library, the librarian knows enough about the subject to translate or they can snag a student to help you.
I think what's happened is that we're seeing students who vape and they are now running these studies.

Figured that would happen. You still need to get published to get an MS or PhD or even MD. So, why not do a paper on something personally interesting?