20 feet away?
I have asthma, and while I understand different people might have different "triggers", the only things that affect me from 20' away are:
mass pollen
extreme seasonal changes
other situations I can't easily escape or wait out because they cover massive areas of effect.
Every other trigger is by contact, or long-term CLOSE exposure. In my opinion, to be affecting this co-worker, you'd have to be hot-boxing your open office, somehow. How many co-workers in HIS 20' radius own pets, wear perfume/cologne, smoke analogs?
On the rare off-chance that your dissipated vape from 20' away IS HIS ACTUAL CAUSE of suffering, it is also in my opinion, that someone with that level of sensitivity had better be well prepared to battle an entire world that is out to kill him. Puff your meds, man. I find it rather hard to believe that, in this situation, there aren't more health-offensive things going on much closer to this co-worker.
Then again, you can always suggest that you can take extra pains to smell like an analog... seems like he wasn't making complaints before the vape?