Someone please explain how freeing half a dozen girls from, oh noes, misogyny make zombies disappear? What, it's suddenly safe because they're now eating MY food? ... However, if it was true and keeping those girls around did make you immune to zombies, then the Last Judgement Gang had the right idea from the get-go :/
Great game; t? I mean, you never find the Portal to Hell to shut here and last time I checked zombies are still roaming around (yes, I researched everything to reach the cure and nothing happened, even with the doctor sidequest).
The only real difficulty is that you cant order your THELs to target mother ships. they focus on small ships and you get overrun no matter how many you have (and I ha plenty :P)