Or we could live like Thoreau and St. Francis.
Or like the holy Anchorites of old.
Or something like the Amish, even.
But no matter. I realize that what I suggest will never happen as a preventative measure.
But if and when a WMD is used on even one city, the people in other cities will begin to move out of their own accord.
Just as centuries ago, when people intuitively left cities for the countryside in times of plague.
You may look up to St Francis and the hermits of long ago, some of whom lived atop huge pillars, many of whom lived in caves and were filthy, flea riddled, and depended upon others for their sustenance, but hardly anyone, then or now, wants to live like that. And in this day and age, since you are so miserable with your plight, that that is your own vision of perfection, I suggest that you follow your heart and try it out. As for it being the only good solution for everyone else, well, it isn't and that's that!
Not everyone, during the Black Plague, left every city it hit and went to live in the country. And yes,some of them survived.
In 1918, nobody left the cities, to escape the Spanish or Swine flu!
And during Elizabeth the first reign people were NOT running away to the country, to escape the many small pox epidemics.
And in a more recent time, people in America were not, not, NOT leaving cities in droves, to escape from wave after wave of polio surges.
A few people left lower Manhattan, after 9/11, but where did they go? Most went to the suburbs; either of N.J. or Conn., or even N.Y., though some did move farther away.
The Amish do NOT live in nowheresville. They live in clusters and rather densely populated villages.