According to uesp wiki:

"Despite supposedly being a percentage effect, characters with 100% or higher Resist Disease can still contract diseases, especially Porphyric Hemophilia and Astral Vapors." It is also considered a bug.

Is this bug already fixed in UOP or it is impossible to fix? I am trying to enchant my armor in construction set with 100% resist disease so i can fight vampires face to face.

In another uespwiki page:
Astral Vapors ignores disease resistance. Characters with 100% Resist Disease and 100% Resist Magic (eliminating the possibility that a Weakness to Disease effect could be added) can be infected with Astral Vapors.
>>>> This bug is fixed by the Unofficial Oblivion Patch.
Similar to Astral Vapors, Porphyric Hemophilia ignores disease resistance as well (This is not a bug, but is by design, introduced in the 1.1.511 patch and later, possibly so that Vicente Valtieri would be certain to give the player vampirism in Darkness Eternal.)

The UOP changes Astral Vapors to account for resistance, but Porphyric Hemophilia is still special.

EDIT: You could create a mod to help with Hemophilia resistance or to remove it. But this would probably involve quite a bit of CS work.