“And I don’t get how they claim zombies overran military positions”
As I understood it, the infection in the WD didn’t spread from biting initially — airborne. Most just got sick and became zombies.
Those that remain are partially immune until bit or die for whatever reason.
See, that was never explained. I understood the airborne-everyone-infected thing, but I didn't know that most everyone just got sick from breathing the virus.
But it would be canonical in terms of Herschel's farm. Genetics shared in the house, except for Otis and Hershel himself, and they just happened to have genetic luck on that one.