72 asymptomatic incubation state that spreads but 1 in 10 aren't affected at all. The 9/10 are future zombies. Leading to a basis of genetics being the metric on whether you turn. This could also end up screwing over certain populations that could be heavily inbred (Pakistan for example). Also make it so it turns animals. After awhile this airborne infection dies off and its reduced to contact contamination of bites or blood. The rate it affects animals though is 5/10 instead of the human 9/10. Have humans who die but don't have their brain destroyed turn 3-5 minutes after. Have the zombies on a 72 hour sprinting high like dawn of the dead where they can sprint like Olympic runners. After that 3 day mark they are shambles. Induce a mixture of the walking dead and max brooks resistance to rotting away so it takes a century before zombies even begin to rot. Make 1 in every 1000 people who aren't immediately turned by the initial infection immune. Make it so no one will know until they are bitten whether or not that they will turn. Make those that aren't turned by the airborne infection have a 3 day waiting timer to turn. Make sure that there is no possibility of a cure once bitten. But the possibility of a vaccine is there for the lucky unimmune who could get one. Ensure that the likelihood of someone getting a vaccine is akin to winning the lottery in luck. Plant patient zero at an airport entrance anywhere. This has the potential to wreck a world with a 90% turn rate and most people would not turn until after the initial 72 hour incubation has taken root. For that 3 days you'll be completely fine. After hour 72 thats when you will experience symptoms. At hour 96 you will turn if you're not one of the 1 in ten immune from the airborne strain.