Eh, microbes get hammered by the pressure wave too. That combined with the fire probably results in pretty much all living things dead in the blast radius.
BLU-96 Fuel Air Explosive bomb. Note that it is being set off several dozen meters away from the two story structure, but the blast wave still nearly obliterates the building. The only bits left are a couple of interior concrete walls.*
Now expand that to a bomb the size of the entire CDC building. The building basically IS the bomb.
Now there ARE problems with the scenario presented in The Walking Dead.
Namely to get a good dispersal of the reactive fuel in a building with so many internal walls you'd have to spray the fuel from nozzles in every room and corridor for a couple of minutes, rather than using a concussive charge to spread the fuel into a cloud like the BLU-96 does. But we saw no evidence of that in the episode - the explosion just "appears", nipping at the heels of the fleeing human survivors. Also, with the fuel at enough saturation to be effective, everyone trying to flee the building should have been choking on the fumes, probably wouldn't have gotten halfway to the exit before collapsing from oxygen deprivation and the noxious vapors in their lungs. And lastly, that grenade they used to open the window should have set off the fuel cloud.
But the blast effect shown isn't one of the problems. If anything, the explosion wasn't BIG ENOUGH, as the hollywood gasoline explosions burn a lot slower than true FAE fuel.
-k
* - Note that the BLU-96 is a 2000 lb bomb. It is hardly the largest FAE bomb the USA fields - that status belongs to the GBU-43 MOAB, which is a 21000 lb bomb. The MOAB is so large that there is no aircraft capable of mounting it on any sort of hardpoint or launcher - instead it is simply tipped out the back door ramp of a C-130 cargo lifter when over it's target.