My favorite take on zombie fiction was a short story that posited that nearly everyone is globally infected, but infection can take one of two forms: form A is

My favorite take on zombie fiction was a short story that posited that nearly everyone is globally infected, but infection can take one of two forms: form A is the regular "undead"-style zombies, but form B merely makes humans stupid. This explains the foolish choices movie protagonists must make for the sake of plot.