White Zones are places where zombies still remain in large numbers, for several reasons such as
1. Lack of military
2. Large population or number of refugees
3. Difficulty in traveling to
White Zones are predominantly cold sub-arctic areas, or cold mountainous areas, or even the ocean floor itself. During the war, the fact that zombies slow down and sometimes freeze entirely in cold weather was often seen as a blessing, as it gave survivors a respite from zombie attacks. After the end of the official war, it became clear that many zombies were still frozen in cold areas, and while their numbers were not particularly large, even a single unaccounted-for zombie could potentially start up the entire global infection cycle all over again.
The most infamous White Zone is Iceland, which is heavily infested even ten years after the official end of the war. Millions of refugees latched onto the idea that Iceland was an ideal bastion of safety, due to its combination of cold weather and isolated island location. Iceland did not have a large standing military, however, and could not possibly screen the millions of infected refugees that overran the country, cramming their way onto the island. The dense concentration of refugees proved ideal for the spread of the zombie infection, until no humans were left alive on the island.
Other sub-arctic to arctic regions around the globe are still considered White Zones due to frozen zombies laying in wait, many of them spread by fleeing refugees, though none were as densely concentrated as Iceland. Much of Scandinavia, particularly its isolated mountain ranges, are still infested; the author of World War Z encounters General D'Ambrosia as he is leading an annual sweep and clear operation in Finland.
Large swaths of Siberia are also still infested; while the number of refugees fleeing to such areas wasn't as concentrated as Iceland, the vast frozen expanses of the Siberian wilderness make it extremely difficult to effectively sweep the entire area for isolated zombies. Ironically, Sibera was Russia's "Safe Zone" during the war because its cold weather and low population density at least kept the zombies relatively in check, but now its huge size makes it an ongoing problem. Many refugees from China and India, often with no winter survival gear whatsover, did try to flee to the isolation of the Siberian wilderness, bringing the infection with them. The United States has offered to help clear Siberia but Russia insists it will be the only one responsible for clearing its own territory.
Sub-arctic Canada is in a similar situation as Siberia, with millions of refugees fleeing north to the perceived safety of the cold wilderness. Many died of starvation in the first winter of the war, but others also brought the zombie infection with them. Sub-arctic Canada is smaller than Sibera so the concentration is denser, though they didn't have to deal with millions of overland refugees coming from China and India the way Siberia did. Even so, the relatively smaller distances meant that millions of refugees from southern Canada and the United States poured into the Canadian sub-arctic. Even ten years after the war, when the author of World War Z visits northern Manitoba, frozen zombies are still to be found. While volunteer organizations claim to be making relative progress, it is very slow and practically not discernable.
Zombies will also freeze and remain hidden in the mountainous regions of countries which are otherwise located in more temperate areas. At the Honolulu Conference some South American representatives complained that the zombie epidemic was retribution against exploitative European and North American imperial powers, because it would be harder to clear their sub-arctic regions. Even other South American representatives dismissed this as just old grievances, however, pointing out that even the Andes Mountains contained frozen and isolated zombies which would be difficult to clear.
Even the Rocky Mountains of the United States had at least some frozen zombies which escaped detection. This was never a major problem, but for up to a decade after the war, volunteer patrols would still find isolated small numbers of zombies every year. When the author of World War Z visits Todd Waino in Denver ten years after the end of the war, a public celebration is occurring because it is the first year in which no new zombie sightings in the mountains have been reported; they remain cautiously optimistic, but do not let down their guard.
The Ocean floorsEdit
The ocean floor can't be cleared because it is physically impossible to send entire armies down there to eliminate them. Zombies can survive under miles of water, in the deepest ocean trenches. Moreover, the vast unexplored size of the ocean floor presents a huge challenge: 70% of the Earth's surface is water. After twenty years, zombies who were originally infected in New York might have found their way to the Marianas Trench east of Japan. Eerily, just as zombies in large plains areas such as the Eurasian Steppe or North American Great Plains formed into "mega-herds" due to the Chain swarm effect, zombie hordes numbering in the millions shamble along in great undead swarms along the ocean floors. Current estimates hold that even ten years after the end of the war, there are at least 30 million zombies still active on the Ocean Floors, making them the greatest number of active zombies remaining in the world by far. This greatly affects maritime traffic, and technically every coastline in the world is still a fenced-off and defended "front line" against the zombie threat.