It’s hard to imagine anything worse than a real cig with regard to the wide scale negative effects it has on nearly every system in the body. Maybe inhaling plutonium. :)
The most harmful part about cigarettes is inhaling byproducts from something burning. I'm even mildly allergic to pretty much every vape product, and I'd acknowledge that provided there is nothing toxic in vape juice, it has to be much less harmful than smoking - simply because of the lack of combustion products.