Vaccination eliminated measles from the U.S. 25 years ago. But it can still spread in pockets where vaccination rates are low, like the west Texas county with a current outbreak. Here's how fast.

The number of people with measles in Texas increased to 146 in an outbreak that led this week to the death of an unvaccinated school-aged child, health officials said Friday. The number of cases — Texas’ largest in nearly 30 years — increased by 22 since Tuesday.