An ongoing measles outbreak that began in one of Texas' least vaccinated counties has mushroomed to 90 cases across a cluster of seven counties in the state, according to an update by the Texas Department of State Health Services on Friday.

Arizona is similarly at risk for measles because the state has several pockets of extremely low vaccination rates, including in Yavapai and Mohave counties, according to school vaccination data from the Arizona Department of Health Services for the 2023-24 school year. Data for the current school year is not yet publicly available.

The measles outbreak in Texas has grown to 124 cases mostly in children and in those who are unvaccinated, according to state data published Tuesday.

Now 124 people infected in West Texas, nine more in New Mexico and outbreak 'still has a lot of energy and steam behind it.'

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