Breathing the particulates that result from combustion is one if not the largest health risk.
I’m a dedicated vaper for at least five years now and have not stopped using nicotine. Anecdotally I can attest to improved breathing health, I can participate in physical activity without getting “winded” as I did while being a combustible tobacco user, cigarettes and premium cigars.
Nicotine use safety aside, the harm reduction from vaping comes from the water solubility of the particulates.
The ‘hand to mouth’ , tactile aspects are satisfied with the mechanics of vaping also. Not recommending vaping for vaping sake , but health wise it is less harmful.
Check out the Sober Vapers threads here on SR for some really good links and info on the science behind the harm reduction.