A zombie outbreak could never happen
According to the movie guidelines, the zombies are slow and fragile, not to mention stupid. fighting and wiping them shouldn't be a hard task, unless like 99.9% of population turned into zombie in one day. Humans should be able to formulate tactics (i mean average humans, not even the genius out there) to counter zombies and the outbreak in general.
Even viruses that spread into air can be suppressed these days.