Well, the problem with the 28 Days Later scenario is the ease at which you get infected. A single drop of blood or bodily fluid from an infected person gets into an open wound or orafice, boom, zombie in less than 10 seconds. This makes killing zombies without like a goddamn hazmat suit difficult. L4D is basically the same deal, except it takesl onger to get zombie'd, boss zombies, and some people are immune. I can't decide which would be worse :x