The first zombie or group or zombies would be gunned down by the national guard. Zombies can barely move faster than a shuffling approach and can be outran by speed walking. Zombies strength in numbers can only happen if they get enough numbers for it to matter, which they won't because they lack intelligence, speed, and they're dead, so they would rot while moving around.
A zombie 'apocalypse' would happen as follows:
Someone becomes a zombie and starts approaching a person, moaning and clearly acting aggressive.
The person runs away, leaving the zombie in the dust. Everyone around the zombie follows suite.
The police arrive and shoot the zombie dead.
Total casualties: 1 person.
Defeating a large plague like this is not as difficult as it may seem. The first step in a proper course of action would be to set up secure locations for healthy citizens as well as researchers who could formulate a working cure for the disease. Once a cure has been formulated, simply fly over every continent releasing the gaseous form of the antibody, and the whole plague will be eradicated within a matter of days. Every disease has a cure, and zombies are no different.
No other epidemic would turn the dead against us. Other plagues killed people and then they were dead and nothing would happen to you. Zombies are like a disease that literally hunts humans. Everyone of our dead would then turn against us making it a lot harder to find a cure when you're trying to run away from zombies.
If a zombie apocalypse broke out in 2010, It would have killed 96% of America's population today.
We know that zombie viruses spread very fast so what's the point in fighting it? No matter how many times we would shoot them, stab them, or even slice their heads off, America just doesn't stand a chance against a horde of zombies.