Embark at a terrifying biome(Scary Biome), make sure there are zombie somethings. Set up a five thick wall around your camp. Never leave the perimeters. All migrants would be wandering survivors, let them in or don't, as they might be infected.

Bonus: If you have "reason" to believe the migrants are infected, sacrifice them to the Armok. Remember, he loves Magma!

Bonus: Only Marksdwarves for defense, You shouldn't get near the zombies, they tend to bite.If they are wounded, they must be quarantined, and shall therefore die.

AdvancedPlay: Add zombie to the creatures list and set them as [EVIL].

Bonus: Send one heroic guy to save the migrants from the zombies, like in 28 days later.

Elf clothing anyone?

Keep a diary from one of the characters perspectives, to be read when the world is repopulated.