To be honest we technically know how people would react in a Zombie/Viral outbreak as it's been tested/shown in a number of games
World of Warcraft had an incident in which apparently some players could contract a debuff of some sorts which was contagious to other players. It was meant to be confined to a dungeon and only affect the party participating however a glitch meant it hit the whole server and this led to an interesting scenario where players not wishing for their characters to contract the debuff fled to less populated areas whilst some players who had the debuff actually went out of their way to spread it in a sort of "Lets all suffer together" thing.
Another game which has tested how we'd react in a zombie scenario is the premise of the text game Urban Dead. That game was about Zombie survival in a large city and what was generally found was that players all united together inside common buildings assumed to be safe, e.g. Police Stations, Mall, Army bases, Prison and players often without communicating pitched in to help one another and worked for everyone's benefit.
So what have these two things told us about any potential Zombie outbreak?
- Survivors will often try to flee to places they associate with some form of order
- People with their own interests will generally still find a common ground to work with others
- Some infected but not yet converted may try to carry out a "Misery loves company" act