The term “patient zero” is overused in bad science fiction and horror. It comes from epidemiology and is an important concept in figuring out where a disease started from and how it spread. When method of transmission isn’t obvious, it is useful in identifying the cause of the spread (like a contaminated water pump). But when you’re just trying to find a cure, any old infected individual (or group of individuals for sample size) will do. And, should you have anyone that is resistant handy, you’re way ahead of the game.
So why do bad movies always try to find “patient zero” in the midst of zombie Apocalypse to find a cure when they’ve got 100s of zombies to sample for tests? I have no idea. There are ways you could write around that to try and make it necessary, but I’ve not found a solution in practice that makes it believable.
The cast tries, but really doesn’t succeed, in making the story credible. Matt Smith (Pride and Prejudice and Zombies), along with his bad American accent, tries to make the most of his role. Natalie Dormer (Game of Thrones) tries, but the script does its best to make a smart woman seem dumb. Fellow Game of Thrones-er John Bradley fares way better in a comic role. Stanley Tucci (Final Portrait) sinks his teeth, no pun intended, into his role more than the rest, but he was given the words to do so. His character is still only a shadow and with limited motivation and value to the story. And Clive Standen (Taken) is just embarrassing as a character and as an actor.
Basically Stefan Ruzowitzky took a weak script by Mike Le and didn’t manage to make anything of it. What you’re left with as an audience is a silly story with a lot of splatter, growling, and yelling. Hey, if that’s your thing, this is your movie. So, despite a potentially interesting cast, this movie is truly something to avoid.
If you want something a bit, ahem, meatier, but with way better results, see The Girl With All the Gifts. That, at least, has a complete story and some solid choices to carry you through.