Zombies are the people of every day, up out of the grave and staggering around in all their droop-lip banality, threatening to infect them, to engulf them, to make them one of their own. The zombie is the guy in the street, a cross-section, as it were, the people you pass every day and look down on. As Chekhov says, "There is nothing more vapid than a philistine petty bourgeois existence with its small change, provisions, vacuous conversations and useless conventional virtue." The walking dead.
Both are diseases. If they break your skin you become one of them.
The kids fear the zombies—but they long to be vampires, to be artists, night people, exceptions, drinkers of blood. H. L. Mencken: "The great artists of the world are never Puritans, and seldom even ordinarily respectable. No virtuous man—that is, virtuous in the Y.M.C.A. sense—has ever painted a picture worth looking at, or written a symphony worth hearing, or a book worth reading."
If there is romantic interest in a zombie, that means that he/she is overcoming his/her zombieness, his/her deadness. Zombies come out of death, until they rot and sink back into it. Vampires go into death, and live happily ever after. It's a class system.