For those interested... Here is a link discussing the latest research
I definitely went through withdrawal when quitting analogs, despite using my e-cig with 18mg e-liquid. So this makes sense to me:
"Six puffs every 5 minutes would deliver the same dose of nicotine delivered by shallow inhaling from one tobacco cigarette every hour". That means 72 puffs of an electronic will give a user the same amount of nicotine as they would get from shallow inhaling one cigarette. He used 16mg e-liquid in his tests