Pre-existing Conditions?

[Zahir ibn Mahmoud ibn Jothan]

So, let's say a 2nd level Paladin, or a 4th level Monk, catches a Disease of some sort.

Let's say it's not fatal.

Let's further assume they adventure on and make a level each. Now they are both immune to diseases, so they can't catch any new ones.

What happens to the ones they had? Are they grandfathered in?

[darkwarriorkarg]

No. They are immune. Accumulated damage still remains