One thing that has struck me in visiting rural towns in Japan is how the graveyards don’t have fences. In fact, superstitious sort that I am, it really freaked me out. However, a realization relieved me of my panic: there aren’t any bodies in there. You can’t have a rise of the undead when there are no bodies.
Now I’m aware that you could still end up with a zombie apocalypse here, of course. After all, most detailings of such an event emphasize its rise among the living, and there are certainly enough living people here. People live pretty close together as well, even in rural areas. But they also tend to be pretty interconnected because of this. The towns have daily announcements that are broadcasted by loudspeaker, and I find it hard to believe a murderer who was as yet not caught would escape those announcements. Though I will say if you got stuck on a train car with a zombie I wouldn’t like your chances.
In addition there is security everywhere in Japan. I had to show my passport just to drive into the airport, much less to fly out. It was honestly really disorienting at the time, and totally unexpected. I mean some of the people with me on that bus were almost certainly Japanese citizens taking domestic flights, and I was just trying to get on a train.
So despite the inherent vector issues, I think Japan would probably be quicker to respond to patient Z than most of us.