This achievement is unlockable using the Necroa Virus.
I played on casual using the following set up: Cytochrome Surge, Creationist, Aerocyte, Xerophile. I started in India and upgraded Air 1, Air 2, Blood 1 and Blood 2.
Once most the world was infected and I had about 50 upgrade points I picked each upgrade on the right until I created Zombies. At this point the option to unlock Air 3 becomes availible and you need to purchase that. Once you have zombies you need to pick up Enhanced Motor Control, Peptide Surge, Dermal Calcifciation, and Cranial Elephantiasis.
It unlocked for me about 1 minute after grabbing all of those abilities.
If you have any questions leave a comment :)