May I suggest you to watch "Common Side Effects" - an very good animated series loosely based on your premises?
Still, highly recommend people watch it. Great animation and art style, good writing and characterization, music is pretty rad and it's quite the trip at times.
Then again, the idea behind "28 Days Later" was that everyone got a cancer vaccine and turned into zombies...
This was not in the movie at all. It was the extremely contagious "rage" virus, inadvertently released by animal rights activists.