Zombie Apocalypse

In a zombie movie, I've never figured out how it is possible for the zombies to be able to multiply fast enough in order to take over the whole world.  Look at it this way, the Black Plague supposedly started in Asia and spread to and was able to wipe out most of Europe, but do you know how long it took for that to happen?  Over a decade.  Another good example is the more deadly but lesser known 1918 Flu Pandemic.  That virus killed between 20 and 50 million people and spread all over the world including the Arctic and remote Pacific islands, but it still took many years to do so.  However, when it comes to zombie movies, the zombie plague seems to be able to overtake the world in a matter of months.  But how?  Sure, you could point out that the modern world has faster transportation like cars and airplanes, but that doesn't take into account that airports have insane security measures and you know TSA isn't going to let some dude who looks like he is on his deathbed onto a plane.  Plus someone infected while driving wouldn't make it very far (b/c according to the bible of zombie books, The Zombie Survival Guide, it doesn't take more than a couple of hours for it to take effect) before they eventually turn into a brain-eating monster.  And don't forget, that zombie will probably be trapped in their car because they are a stupid brain-eating monster.

On top of that, can you think of the most recent deadly outbreaks that struck somewhere in the world?  Ebola?  Swine flu?  Do you remember those spreading all over the planet and killing millions of people?  No, because we have something called the Center for Disease Control that is specifically designed to prevent such outbreaks.  So, if a zombie virus were to come about you know that the CDC would be all over that shit and shut down those slow moving bastards before they ever have the chance to wreak havoc on the unsuspecting public.  Which brings me back to my initial point, how is it possible for a bunch of slow, easy head-shot targets to take over the world when they wouldn't even be able get out of their own town before some government agency rolls up and quarantines the whole place?  They wouldn't.  Which I guess is the reason most zombie movies have to say that an evil corporation spread it worldwide, but even then, where in the hell is the profit in that?  Do they have a cure to sell?  Maybe, but what good is a cure for a bunch of undead customers?  It's not.  They're already dead.

"This is the only way the zombie virus could spread worldwide and I'm fairly certain that that plane would never make it off the ground with a dude stumbling around biting people."