The measles outbreak that began in West Texas has now grown to well over 100 cases, with confirmed cases across Texas and New Mexico and possible exposures as far away as San Antonio and San Marcos. From the ongoing outbreak,

A Texas measles outbreak has doubled in the last week to 124 cases, state health officials said Tuesday, a day after they warned a person infected with the highly contagious disease had traveled from the outbreak zone.

Texas is in the midst of the worst measles outbreak in decades, with 90 cases across 7 counties. Here’s what to know.