White Box Zombies by Bloat Games is everything you need if you want to include a little thing like the zombie apocalypse into your White Box game (perhaps as the result of Death Frost Doom). At 48 pages this is a pretty meaty pdf (especially at the current sale price of $2.00).
The book begins with zombie infection rules. These are pretty deadly but it's essentially get bit/clawed by a zombie with it, make a save or die and become a zombie. This is pretty intense, but no one said zombie apocalypses were for the weak.
We are then presented with a the Classic White Box Zombie and a brief discussion of why it's different than one of the new infection causing zombies. After this we get into the Infected Dead. Stats are given as well as a suggested pack size. These are the infected (with a brief description or what they remind me of):
Living Dead Zombie (classic Romero shamblers)
Groaners (tougher classic Romero shamblers)
Walkers (weaker Romero shamblers, similar to Walking Dead zombies)
Runners (Dawn of the Dead remake)
Rage Zombies (28 Days Later)
Fleshless Zombies (the Tarman from Return of the Living Dead series)
Screamers (7 Days to Die, they have a scream that can paralyze players with fear and attrack other zombies)
Bone Zombies (Dry Bones from Mario, skeletons from Castlevania)
Mutated Bone Zombies (what happens when multiple Bone Zombies combine)
Boss Zombie (Dawn of the Dead remake, but stronger and more cunning)
Legend Zombies (unique intelligent infected)
Melting Zombies (advanced decayed zombies that have acidic goo)
Zombie Children (Cooties)
After the special zombies we're treated to a page with demihuman and monster infected zombie rules. This is followed by a collection of demihumans and monsters. We get (living) stats for the monsters, as well as two infection zombie variants (from the group mentioned above). The demihumans/monsters presented are bugbear, centaur, dwarf elf, cloud giant, firbolg, fire giant, frost giant, hill giant, stone giant, storm giant, gnoll, gnome, goblin, hobgoblin, kobold, lizardman, ogre, orc, and troll.
I just picked this up recently and haven't used it, but I'm very happy with the pdf. It's a lot of great material for a cheap price. Infected zombies are pretty deadly, but that's to be expected (especially in the OSR).
If you want a preview you can check out the (by request) Dark Elf Zombie. This includes White Box stats for Standard Dark Elves and stats for Legend Dark Elf Zombies and Screamer Dark Elf Zombies.