Krona’s plans included going to Oa with the entities, at which point he goes ahead and lets the Entities choose the Guardian of their choice as a host. All of them but Parallax do so, as Parallax is returned to the Central Battery to restore the impurity in the rings.
With the impurity restored, all Alpha Lantern’s are taken offline, while every other Lantern is brought under the thrall of Krona.
Who is immune to this? Lanterns who have had previous dealings with Parallax and his particular form of infection. Hal, Guy, John, Kyle, Kilowog, and Ganthet.
Though after reading through both parts one and two, it seems only Hal is truly immune to infection, as even Kyle who formerly hosted Parallax was feeling the effects of the fear demon infecting his ring.
Tags: Green Lantern (Hal Jordan), Green Lantern Corps, Krona, Spoiler Warnings, War of the Green Lanterns