Quick tips (for harder): 1: ignore graveyards, waste of time to attack, left one that started next to my fort alone the entire game
2: you want to avoid the evil graveyard and city hall to get less zed on your walls until you have the cure
3: antivenom is amazing it's worth it to research the soldier line before any of the others it gives a 10% boost to all soldier effectiveness ratings, defense and attack both
4: Be aggressive, continuous attacking seems to forestall zed assaults, I was only attacked twice, excluding hordes, when I kept at least one tile under attack every turn. Also, the losses didn't hurt that much because of how fast I was taking territory and recruits in by the time the zed started attacking.
5 (probably bogus): Name your city Kamloops, I haven't lost yet with that name (3-0), and I've never lasted more than 40 turns with any other name (0-6)
Finally infected Madagascar, and I sit here thinking YESSSS!!!! then Peru closed its borders, which are the only way in, without anyone infected in it. :(
Hahaha I was playing a game on hard where I was trying to kill off all of the scavengers but leave the rest of the people alive and training them to be something else didn't count, I sent my last 4 scavengers (I'd already picked up all the recruitable survivors) with 0 soldiers/anything else against the overrun city hall and they all came back alive. They killed as many as 4 soldiers would have too.
 "Tactical Assassin 2"){kind=icon}
 "Rebuild"){kind=icon}
 "Pandemic 2"){kind=icon}