To sum up the explanations John and ANI provided:
The Malnosso were fiddling with the barrier and did something wrong. We became 'unprotected,' and this led to certain individuals being possessed by the spirits. The new forms assumed -hybrids, as he referred to them- are considered abominations; they were apparently so dangerous, the Malnosso decided that death was the only solution. John made an agreement with them, and somehow flushed the spirits' influences and repaired the barrier. Those affected are feeling ill as an aftermath, but have returned to how they were before.
Facts
-John referred to the hyrbids also as a form of evolution.
-The Malnosso are familiar with whatever the hybrids are, and fear them.
-The spirits weren't "meant" to exist.
-ANI said the effects of this phenomenon are world-wide (those within the Malnosso were also affected, and detained).
-The weakening/altering of the barrier allowed this to happen.
-John can repair issues with the barrier the Malnosso can't, and raise barriers on his own.
-Most affected had a certain affinity with the spirit that possessed them.
-Most of the unaffected didn't have any sort of elemental affinity.
My conclusions
-Those affected outside the barrier are still affected.
-Whatever the affected turned into are somehow related to whatever the Malnosso believe they're "protecting" us from. Possibly the third party itself.
Any input from anybody?