The number of measles cases in the U.S. has reached its highest point in more than a decade.

At 131 cases, the figure is still small. But that's just for the first seven months of this year and doctors are troubled by the trend. There were only 42 cases for all of last year.

Nearly half of this year's cases involve children whose parents rejected vaccination. Pediatricians are frustrated, saying they have to spend more time convincing parents that the shot is safe.

A review by the Centers for Disease Control and Prevention finds that a number of cases involve home-schooled children who aren't required to have the vaccines.