He's not saying that zombie epidemics as a topic are over, just that his take on it has been rendered obsolete by current events. It's sort of like a short short (either written by or edited by Isaac Asimov, I don't remember—I read it forty years ago) that proposed that Everest would never be summited because it had been colonized by Martians. Between acceptance and publication, Everest was summited.
Another similar instance just popped into my brain—in college a friend wrote a piece for the college paper in which, writing about political changes in Eastern Europe, he wrote, "but don't expect the Berlin Wall to come down any time soon."
As you might have guessed, the Berlin Wall came down between the writing and the publication.
I stumbled upon a paper I wrote in high school in 1987 about European unification. I came to the same conclusion; thankfully no one but my teacher ever read it, and I doubt she remembered it 2 years later.
