Disease Control got lucky. The first waves of undead hit everything hard. Infrastructure, the military, pretty much everything disappeared in a few months. CDC had makeshift labs set up in Yosemite National Park, and was able to catch some dead hikers who'd perished in the woods. Every single resource they had went into finding out what the hell was doing this. Initial scans (see above image) told us nothing. Deep in the woods, hidden from the world, it was a race against extinction...