Though the book and movie diverge with regards to certain details, one thing clear in both presentations is the fact that, before it was perceived as a global crisis in need of a unified response, individual countries dealt with the zombie outbreak with their own national self-interest as a priority. Various elements of the World Health Organization would have likely experienced pressure/coercion of some type from numerous global factions trying to take advantage of the situation. Before Gerry regained consciousness and revealed who he is working for, the only source of information available to the WHO doctors was a soldier (injured but armed) from one of the few remaining places (Israel) known to have some success holding off the zombie plague without completely succumbing as the rest of the world did. An emissary from those in a desperate situation, accompanied by an armed escort who has managed to travel half way around the world when being out in the open is a virtual death sentence, is unlikely to have pleasant intentions. So, it is reasonable for the WHO personnel to be suspicious. Edit