This was, while slightly unrealistic at times (zombies excluded), really good for a short read. I could honestly see this being adapted into a 5-minute per episode anime series. In a wierd way, especially with that ending, it almost seems like it could be a precursor to an entirely different story altogether.
The vaccine stuff is a bit goofy but its interesting and what else can you write about if the MC is going to hermit in a convenience store. My only complaint is the odd ending.