During the game, there are several instances where someone is sure they can remove the tadpole, only to find that these are different. The question here is, if this was due to the Absolute's active protection, or the nature of the tadpole and its link to the host.
Well, technically, most of the assurances of removal are just "I'm going to kill you, but I'll say it's a cure".
Ormeluum is the only one who genuinely thinks he can remove the tadpole, but he mentioned that these are different and are protected by magic (The Absolute's protection)
The Astral Prism protected the Emperor's chosen from being turned by the Absolute, which could be read as a clue that this is something the Absolute had to do consciously, i.e. keeping True Souls humanoid, while choosing to turn others earlier. Without that trigger, an infected host would stay in suspended ceremorphosis.
During one of the encounters with the Dream Guardian, it is mentioned that "The signal for you to turn is being sent repeatedly". Signifying that the act of ceremorphosis requires the Nether Brain to actively decide for it to occur, or at the very least, this Absolute brain (It doesn't make much sense for regular Brains to need such an active role given their lack of desire for un-ceremorphed hosts, evidenced by the fact that everyone and their cat tells you that ceremorphosis happens very quickly after infection and that you are walking around normally is highly irregular)
Which brings up questions in regards to what would happen post-brain. If these tadpoles are (Mostly) dormant until given the order to go full ceremorphosis... Will that persist once the brain is gone and they will just happily sit inside your brain forever as they can never receive the signal to turn you? Or would they default back to regular tadpole behaviour and just insta-consume you?