Aerinah

Answer: Gerry gets an idea on the plane: he has noticed the zombies ignore some people, and realises this could be because they somehow sense those people have a life-threatening disease or infection and thus are not ideal carriers of the zombie plague. So, maybe such diseases can be used as camouflage (as long as they're treatable): if you infect someone and then give them the cure, they will live but will still have the disease in their blood, meaning (hopefully) that the zombies won't attack them. This doesn't cure or kill the zombies, but it will "hide" people from them if it works, keeping people safe and giving them time to deal with the zombies some other way. He realises he needs to find a place where deadly diseases are studied (and therefore where there will be live samples of the diseases), so he calls Thierry and has him find the closest such place that the plane can get to. This is the WHO lab in Cardiff. As he explains to the scientists there, he wants to get some of their deadliest disease samples from the vault, infect someone with one of them, and then expose them to a zombie to see if the "camouflage" works. He gets trapped in the vault, though (by the zombie who will kill him as soon as he opens the door), so he has no choice but to infect himself and hope his idea works. He injects himself with some disease (we don't know which), waits a while for it to spread throughout his bloodstream, and then exits the vault. And it works: all the zombies ignore him because they can now sense he has a deadly disease and is no longer a good host for spreading the zombie plague. When he gets back to the others they inject him with the cure...but the disease is still in his bloodstream so he will remain "invisible" to the zombies.

Aerinah