One more thing I'd like to point out is that I've watched friends switch from smoking to vaping and they often will begin to chain vape even though they never chain smoked. It's not as smelly, you don't have to light another one and it's just much more convenient. That's not healthy, these people become even more addicted to nicotine than when they were smoking 'analogs' or what the common folk refer to as cigarettes.
Eh, maybe.
Remember that it's been shown that your lungs only absorb a portion (anywhere from 20% to 50%) of the nicotine in the liquid.
Are we more addicted to nicotine, or are our brains realizing that we're short changing it on it's nicotine cravings on every puff? If the latter, it makes sense for us to vape more than we would have smoked, even if we're getting the same nicotine.
For the OP: nothing is "healthy." In fact, the term is not even really defined. If "health" was an actual measurement, we could say, for example, that a type 2 diabetic could be more or less healthy than a person with a blood clotting disorder. Considering that comparison is nonsense; it's easy to realize that health is a personal and circumstantial thing.
Is our heart beating "healthy" considering that each beat is one beat closer to our death? What about cell reproduction when you consider that cells are designed to only divide x amount of times before killing off its host?
No, "healthy" doesn't exist. The question is, instead: is the usage of vaporizers going to cause either death or lack of quality of life _within_ the amount of time it would take for you to have died from other causes? We won't really know for sure for about another 60/70 years. Within that time I am expecting valid health concerns to be presented about vaping. Will these health concerns be as bad as those proven to be caused by analogs? Nobody really knows, but virtually everyone, including doctors who study this stuff, say that the harm reduction is absolutely real.