The following study from Dr Riccardo Polosa looks very promising
Researchers at the University of Catania, Italy, and the University of California, Los Angeles, headed by Dr. Riccardo Polosa, undertook a study of young vapers for 3 1/2 years. These vapers never smoked. The study measured coronary, circulatory, and pulmonary vital signs. Comparative studies were also made against those that do not vape or smoke. (I first sighted this article at Vaping 360.com)
Whilst the report concludes that 3 1/2 years of vaping shows no harm to the end-user, and more long-term studies are needed, the news is indeed positive, especially for those who plan/hope to vape relatively short-term.
Rather than copy and paste the whole report, here is the link. https://www.nature.com/articles/s41598-017-14043-2