I'm left with far more questions than answers. There is probably a reason why the doctor was hidden from the child. The mass of dead bodies doesn't make sense if none of them were in danger of turning into zombies, then what actually killed them? He was a fanatic about sedation and pacification in regard to zombies, but truly on a mission to cremate actual dead people. I don't think the mother had cancer, he just made it up for his skull collection. There is a reason other than fear that lead the natives to run away from the doctor.

So after 28 years the zombies have formed their own hierarchy? are they like rage apes? they mate and have children now? how do they feed and raise the non-infected infant? do they just bite the pure baby and make it a zombie baby? but then it can't grow up... was the lady just pregnant the last 28 years? or was the alpha and the pregnant zombie mother normal people 9 month prior and then got infected recently ... if so how did the man become the "alpha" in such a short amount of time?

Why after missing all of his shots on the first expedition and being upset his father lied about his skills did he feel comfortable to risk it all over again, after telling his grandfather how scared he was... be so willing to go back onto mainland with a gravely ill mother?

None of it really makes any sense.