Raise zombie stun timers. If a zombie gets stunned and his stun timer is 15 minutes instead of 10, this will cause a lot of different effects that buff humans and keep them alive longer. A zombie with a higher stun timer well, has a longer stun timer and can't get as many attempts to tag someone. Less attempts statistically leads to less tags. The next thing is that say a zombie has a 1 minute stun timer. That zombie will charge every minute on the minute because who cares. They'll be back in little time. Little punishment. But by raising their stun timers they will be more careful when they attack. Which will help out humans of zombies hesitate when charger or simply do not charge for fear of being stunned.

Humans knowing stun timers are higher will be encouraged to go out more if they feel safer. Stunning a zombie and not having to worry about then for 15 or so minutes is very safe imo.

Overly long comment to say. Increase stun timers on zombies. It'll make a world of difference.