Triggering a Datapack ONLY when an Effect is active (1.21.1)

Basically the title. How do I make it so that everything in the datapack ONLY applies when a certain Potion Effect is in place? Specifically, let's say I have a datapack that modifies mob spawns, making them more or less frequently, so I only want this to be active when the player is under certain Potion Effects, such as let's say Blindness. How would I make it so that the datapack spawn modifications stop and go back to normal once the Effect wears out?