Learning that Gabriel is almost definitely suffering from a flu is also pretty frustrating, since The Walking Dead was seemingly leading audiences to believe that the previously teased radioactive waste would come into play, since Gabriel potentially covered himself in the guts of walkers who’d come into contact with the waste.
While somewhat ridiculous, radiation poisoning would be an all-new way for The Walking Dead to kill someone, and the repercussions of such a threat could create unpredictable story blips for years.
But if Father Gabriel’s sickness is explained away by a common illness like the flu, everything about that plotline would feel a lot more meaningless.