Person A is part of a military mission. Told to protect a few very populated cities so that the outbreak doesn't get to the people, not wanting to lose a heap of civilians. As person A works, the outbreak gets worse near the city they are in. People have started dying and he and a few others are forced to stay near an area that was heavily populated with the reanimated dead. They are on a shift where they would watch the group every few hours between the night.

Person B had stayed home the whole time, since the apocalypse and outbreak news had started. They weren't ready for the thing to go downhill. Person B stayed inside until they started to run dangerously low on food. Forced to leave their home, person B travels to find a market or somewhere to get food and soon enters the heavily populated dead area without knowing.

Continue on! :D You don't really need to follow the scenario, have fun!