Brand Passive Vs Vlad W

So i just played a game as brand vs a vladimir and i proc'd my passive 3 hit ability where the ring of fire starts and then detonates dealing . Im unaware of this but vlad pool'd and was able to avoid the damage from the detonation of my 3 proc passive. Is this suppose to be this way riot? If something like ignite is able to do dmg to vlad while he is pool'd i would hope that my burn dmg and passive dmg would also work. Please clarify this as i hope you reward brand players for hitting 3 abilities on vlad isnt negated by 1 ability.