In 2009, US suffered from an outbreak of a virus named the Green Flu or scientifically known as KALIVIRUS-09. This virus caused a huge mass of destruction in the East of US, and the government decided to close the infected region entirely, leaving both survivors and infected alike trapped to their luck.
The survivors fought bravely, where two of known groups even met. The first group composed by Louis, Francis, Zoey, and Bill; met the second group after the bridge where the first group was located was fixed after Bill sacrificed himself for his group to escape. They didn't leave and remained to help others as they did to the second group for them to leave that place, and after helping them, the first group finally escaped in a boat to that desired life in an isolated island as they wanted.
The second group composed by Ellis, Nick, Coach, and Rochelle; escaped the bridge with the help of the first group and progressed until reaching another one where the military was waiting them to rescue them, or so they thought. They went through the bridge, and then the military bombed it to unable the infected from leaving the rehionregion and spread the virus, while taking the second group.
The US managed to hold the virus inside US, and killing all remaining inside the region, while experimenting with the second group. But the virus remained as the first group started living in the island, the virus mutated when fell into the water outside US thanks to the first group, what made it mutate and can spread through water and ocean animals. Luckily, the virus couldn't actually affect animals, but that didn't stop it from using them as infection way.
After many years, the virus did spread further by the reproduction of the dishes and jumping from one to another. This process was slow, tedious, but constant, and after a decade, did finally reach a destination, UK. And from there, the virus moved very quickly to further and easily reaching Europe. One of those places to be hit so quick, was Spain, in the quarter trimester of the year of and near of 2024.