Psychological horror. A deadly pandemic forces two families together, and you learn that people are worse than the disease.
The family journey feels a little underdeveloped: they interact positively for relatively little before it goes south into distrust.
My mild theory is that Joel Edgerton's son got the disease from the dog who got it from the grandfather, and his dream sequences are a mix of nightmares and sleepwalking (which is alluded to be one of the symptoms). But there are a lot of holes in that theory, as it is very unclear how the disease spreads, and along what timeline.
The juxtaposition of trust (Will) and suspicion (Joel) is stark and well done. But it does make you wonder what the "right" action is in a situation like this. Despite all their trust and their distrust, both families lose in the end.
I thought it was decent, but not great.