The zombies of the WWZ film are all victims of a devastating virus of unknown origin. No one knows how the infection began, but within weeks it spreads rapidly across the planet, threatening to drive mankind to extinction. As entire countries fall to the undead onslaught, the remnants of the US military work toward finding the source of the virus and a means of curing it. It is discovered towards the end of the film that the zombies only attack healthy human beings, completely ignoring those who are critically ill. Eventually, a medical defence against the infection is devised using samples of highly lethal diseases taken from a World Health Organisation lab in Wales. This is not a vaccine, as such, but more of a repellant. Humans given this treatment are able to go about freely while being completely ignored by the zombies, since zombies only attack people who do not carry any prior illness. This allows the remaining militaries of the world to fight back against the zombie masses and slowly take back their territory.
The zombies of World War Z do not appear as rotten and decayed as most other zombie types, though this may be due to an insufficient amount of time passing since the pandemic began. Infectees may not stand out from normal humans from a distance, but up close the differences are quite apparent: the skin of the infected subjects is noticably withered as though dehydrated, particularly on the face where the skin seems to stretch around the skull. The eyes turn deathly pale and the subject's blood darkens.
Unlike classic zombies which can only shuffle slowly, these zombies can run at an athletic pace. Since they are technically dead, they do not tire and can rush towards prey without needing to stop for anything. Rather than the low, guttoral moaning of standard zombies, these zombies constantly emit a ghastly, ear-piercing scream when hunting. They also do not seem to hunger for living flesh as they are always seen to bite victims once before moving on to find new prey. Being driven by the virus that transformed them, zombies are compelled only to seek out other humans to spread the infection. People who are bitten succumb to the virus rapidly and witnesses have stated that victims change in as little as 11 seconds. In the 11 seconds before total zombification, victims convulse violently as the virus ravages their nervous systems.
Zombies are utterly mindless and lack any sense of self-preservation, attacking any uninfected persons regardless of obstacles or attacks upon themselves. They are highly sensitive to sound and will be attracted to any source of noise. They are nearly always encountered in vast swarms and can quickly overrun areas as they almost literally flood through. Even the highest barriers will not deter them, as shown when countless zombies pile on top of each other in order to get over the walls surrounding Jerusalem.
Like other zombie types, these zombies can only be killed permanently by destroying the brain. Also, they are somehow capable of sensing whether or not someone is diseased and completely ignore persons who are terminally ill such as cancer sufferers.