The Texas health department said all but 23 of the cases are patients ages 17 and under. Eighteen people are hospitalized.

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.

State records show 26 Bexar County school systems have measles vaccination rates below the 95% required for herd immunity. Most are private schools and charter schools.

The measles outbreak in rural West Texas has grown to 124 cases across nine counties, the state health department said Tuesday, and 18 people are hospitalized.

Nine of the state's counties have now reported cases, though most infections are from the Gaines County epicenter.

State and local health officials are urging individuals to receive MMR vaccine as Texas reaches 124 cases this week. Here is what we know.