Carriers wasn't a horror film. If you were expecting a horror film, you were going to be disappointed.
The movie wanted to be about the loss of humanity, and how far people are willing to go in the interest of self-preservation; unfortunately, the characters never got deep enough to flesh out the idea of what "humanity" consists of, until they tried to rush it in the last 15 minutes of the film, and by that time it was too little too late.
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