I'd thank them for their concern about my well being and tell them I'm not sure if/when i'll quit. I'd explain that i'm taking a calculated risk and the outcome is most certainly better than the alternative (ie analogs). I've not come across any definitive proof yet that vaping is harmless, but odds are very high it's better for me than analogs. I wouldn't get snarky or rude with them, they very well may be showing genuine concern.