It's weird that there are people on the net speculating that the virus is mutating and has infected the pig. I don't think there's any sense in the writers going with that kind of plot - I thought it's already been established that everybody already has the infection, and it just kicks in when they die. They can't get infected because they already have the virus.
I bet the kid with the glasses just died because he was sick from something. Probably the same disease that killed the pig, but it's not the zombie virus.
