This story is amazing. I see people complaining about the ending being confusing or stupid, but seriously? That's the only ending that makes sense. Consider the themes of the story, the premise of "everyone has one day to live", the fact that we all have been asked that question, and that we all have our plans in that eventuality. The fact is that the unseating of that premise at the very end is the only way for this story to happen. No, seriously! Otherwise, the rationalization of the premise remains dominant and, much as how people have these dumb plans about what they'd do in a zombie outbreak, the story just becomes a montage of "and then the rational humans did what we all know we'd do" rather than what it clearly is from page 1, which is a story of "hey, these plans we rational humans have... they're kinda dumb, aren't they?"
The story is ultimately optimistic about humanity but pessimistic about the society we've set up. Near the end, when the family reunites and everyone recognizes that the materialism of modern society has detracted from our ability to pursue any happiness that doesn't also make someone profit... all that stuff they're saying isn't wrong! Or at the very least, it's persuasive, and therefore well-executed by the author. The final horror doesn't come from the virus, or from the violence that panicked masses express, it comes from the vaccine. Death is not a forced choice anymore, and most people will take the vaccine, but what that means isn't simply coming to terms with the consequences of their actions, the dumb plans they made. The vaccine means that they'll all be forced back into the society that motivated their unhappy actions at the beginning of the story. There is no third option, no way to live a genuine life in the philosophy set out near the end. There is only society... or death.
Study hard, kids!