A child who was hospitalized with measles in Texas has died, state health officials said this week. It marks the first death in the state's latest outbreak — the largest such outbreak in close to 30 years — which has left at least 146 people infected.

Gaines County in West Texas is at the heart of the ongoing measles outbreak. Non-medical vaccine exemption rates there are high.

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.