Part of an image from NIH depicting so-called "herd immunity." Measles outbreaks can more easily occur in communities where numbers of immunized people has dropped below a critical mass.
NIH Image Gallery
And why we continue to turn to Mr. Rogers years after his show went off the air.
China has said that within the next few years 80% of households will be connected to the internet via fiber optic cable, which provides a much faster and more reliable connection. In the U.S. that number is about 10%.