Vaccinations are only as effective as the percentage of the population that gets them. Your grandma getting one doesn't help if you're around her and have the flu. If 100% of people are vaccinated then there is less a risk to the general population than if only 50% have it.
Good find, make sure all you crazy people select "Fast" at the bottom :-D I missed one on the signs test, I've never seen a "no hitchhiking" sign before lol