Kept my interest, but lots of questions unanswered "Some Spoilers"

I liked it, liked the premise, but as others have pointed out, lots of questions/plotholes. I just accepted the admittedly silly notion that the government epoxied all the doors in the middle of the night, for the sake of moving the plot forward, but the one thing that stuck in my head early on was why did they turn off the water/electricity? I can see their logic of cutting off phones, blocking cell signals, and presumably cutting internet but what purpose does shutting off utilities serve? The virus doesn't spread that way and if you've shut off communication, then why?

The other one that bugs me is near the end, as Mark and the boy and Enid were leaving the building after the gas went off, Mark barricaded the doors so that the mob was trapped inside with the gas. That seemed out of character to me, that particular mob wasn't after them at that time, wasn't even really paying them much attention. Maybe it was just because someone in the mob might be infected, because I don't think Mark would think they should be gassed. Seemed unnecessarily cruel.

And of course the ending was strange. My first thought was actually that the government had maybe staged the whole infected thing to steal all the kids for some nefarious reason, I didn't pick up on all the kids being mute? Anyway, could have been a much more satisfying movie had some elements made more sense, or been explained better.